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DC Plumber practice questions

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Question 1Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

The District of Columbia adopts its plumbing regulations primarily through which document, as amended by local rulemaking?

  1. The National Standard Plumbing Code
  2. The Uniform Plumbing Code
  3. The International Plumbing Code Correct answer.
  4. The National Plumbing Code of Canada

Explanation

The District of Columbia Plumbing Code is built on the International Plumbing Code as the adopted model code, with District-specific amendments issued through rulemaking. Local amendments control where they differ from the model text.

Question 2Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

Under the District's plumbing regulations, who is authorized to obtain a plumbing permit for work on a building's drainage system?

  1. Any registered architect for the project
  2. Any property owner regardless of occupancy
  3. The licensed plumbing contractor responsible for the work Correct answer.
  4. The building's tenant with written landlord consent

Explanation

Permits for plumbing work are issued to the licensed contractor who will perform the work, who must be licensed in the appropriate trade. Owner-performed work is limited to the owner's own single-family residence and still requires the owner to meet code requirements.

Question 3Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing fixture is installed in a room that contains a fuel-burning appliance. Which code concern drives the requirement for combustion air and venting review in that space?

  1. Cross-connection between the drainage and vent systems
  2. Fixture clearances to the appliance
  3. Backflow protection for the water supply
  4. Adequate combustion air and relief of flue gases Correct answer.

Explanation

The mechanical and plumbing provisions require that fuel-burning appliances receive adequate combustion air and that flue products be safely vented. Locating a fixture in the same space does not by itself protect the appliance from air starvation or spillage.

Question 4Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the minimum required air gap, measured vertically, between the lowest point of a water-supply outlet and the flood level rim of a fixture?

  1. One inch or twice the effective opening, whichever is greater Correct answer.
  2. One-half inch regardless of opening size
  3. Equal to the diameter of the drain serving the fixture
  4. Two inches for all fixtures

Explanation

The code requires a minimum air gap of at least twice the effective opening of the outlet, with a floor of one inch. This prevents backsiphonage even when the outlet is close to the flood level rim.

Question 5Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building drain receives discharge from plumbing fixtures and conveys it to the building sewer. Where does the building drain terminate?

  1. At the vent stack connection
  2. At the property line
  3. At the first manhole in the public right-of-way
  4. At the point where it exits the building foundation wall Correct answer.

Explanation

The building drain is the lowest piping of the drainage system and extends to a point outside the building wall, where it becomes the building sewer. The building sewer then continues to the public sewer or private disposal system.

Question 6Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

Which fixture is required to be connected to the drainage system through an indirect waste receptor rather than a direct connection?

  1. A commercial coffee urn Correct answer.
  2. A water closet in a public restroom
  3. A residential kitchen sink
  4. A bathtub in a hotel guest room

Explanation

Commercial food and beverage equipment such as coffee urns is typically drained indirectly to prevent contamination of the drainage system and to allow the equipment to be removed for cleaning. Domestic sinks and sanitary fixtures are directly connected.

Question 7Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the purpose of a trap primer in a plumbing system?

  1. To vent the trap to the building exterior
  2. To maintain a water seal in a floor drain trap that rarely receives flow Correct answer.
  3. To increase the flow rate through the fixture drain
  4. To add chemicals that dissolve grease in the trap

Explanation

A trap primer supplies a small, metered amount of water to a trap, such as a floor drain serving a mechanical room, so the trap seal does not evaporate. Losing the seal would allow sewer gas to enter the building.

Question 8Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

Which of the following is the correct designation for the vertical pipe that conveys sewage from water closets and other fixtures above to the building drain?

  1. Soil stack Correct answer.
  2. Storm drain
  3. Relief vent
  4. Vent stack

Explanation

A soil stack is a vertical drainage pipe that carries the discharge of water closets and other fixtures down to the building drain. A vent stack serves venting, not drainage.

Question 9Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A 4-inch horizontal building drain is installed at a slope of 1/8 inch per foot. Is this acceptable under the code's minimum slope provisions for a 4-inch drain?

  1. No, 4-inch pipe must slope at least 1/2 inch per foot
  2. Yes, but only if the drain is less than 10 feet long
  3. Yes, 1/8 inch per foot is the minimum permitted for 4-inch pipe Correct answer.
  4. No, 4-inch pipe must slope at least 1/4 inch per foot

Explanation

The code permits 4-inch and larger horizontal drainage pipe to be installed at a minimum slope of 1/8 inch per foot where the developed length and available fall allow it, though 1/4 inch per foot is the general minimum for smaller pipe. The engineer or installer must confirm the slope carries solids adequately for the run.

Question 10Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A horizontal drainage branch serving a single lavatory is 1-1/4 inches in diameter. What is the maximum developed length permitted for a trap arm of this size before a vent must be provided?

  1. 3 feet
  2. 6 feet
  3. 5 feet Correct answer.
  4. 8 feet

Explanation

The code table for trap arm length limits a 1-1/4 inch trap arm to a developed length of 5 feet, measured from the trap weir to the vent fitting. The limit protects the trap seal from pressure fluctuations.

Question 11Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A lavatory drain connects to a vertical drain stack. Which fitting arrangement is required to prevent the lavatory's trap seal from being siphoned?

  1. A sanitary tee with the branch entering the stack above the fixture's vent connection Correct answer.
  2. A sanitary tee with the branch entering the stack below the fixture's vent connection
  3. A double sanitary tee serving two lavatories on opposite sides
  4. A wye with the branch entering the stack at 45 degrees below horizontal

Explanation

A fixture drain must connect to a vertical stack through a fitting that prevents siphonage. A sanitary tee with the branch above the vent connection and the flow turning downward keeps the trap arm vented and avoids the siphonage that occurs when the branch enters below the vent.

Question 12Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A water heater is installed in a building's basement without a relief valve discharge pipe routed to a safe location. What does the code require for the temperature and pressure relief valve discharge?

  1. Discharge directly to the drainage system without an air gap
  2. Discharge to a point no more than 6 inches above the floor with no receptor
  3. Discharge to a floor drain through a trapped line
  4. Discharge through an air gap to a receptor or to the exterior Correct answer.

Explanation

The relief valve discharge must terminate through an air gap into a receptor or discharge to the exterior so that a blockage cannot back up into the valve and so that scalding water is discharged safely. A direct connection to drainage is prohibited.

Question 13Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A backflow preventer is installed on a boiler feed line. Which type of device provides protection against both backsiphonage and backpressure?

  1. Atmospheric vacuum breaker
  2. Pressure vacuum breaker assembly
  3. Double check valve assembly
  4. Reduced pressure principle backflow prevention assembly Correct answer.

Explanation

A reduced pressure principle assembly protects against both backsiphonage and backpressure because it includes two independently acting check valves plus a differential relief valve. Boiler feed lines and other high-hazard connections typically require this level of protection.

Question 14Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building's water service pipe is 2 inches in diameter and supplies a building with a peak demand of 60 fixture units. Which factor most directly determines the minimum size of the water service under the code?

  1. The developed length of the service and the available pressure Correct answer.
  2. The diameter of the building sewer
  3. The number of water closets in the building
  4. The building's total floor area

Explanation

Water service sizing depends on the demand in fixture units, the developed length of the pipe, the available pressure at the source, and the pressure required at the fixtures. The code sizing tables combine these factors to establish minimum diameter.

Question 15Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A vent stack serving a group of fixtures extends through a roof in a region subject to freezing. What is the minimum required extension above the roof surface?

  1. 24 inches above the roof
  2. 18 inches above the roof
  3. 12 inches above the roof
  4. 6 inches above the roof Correct answer.

Explanation

The code generally requires vent terminals to extend at least 6 inches above the roof surface, with greater height where snow accumulation is a factor. Local amendments may specify additional height in areas with heavy snowfall.

Question 16Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A floor drain is installed in a public restroom and is not expected to receive regular flow. What is the minimum trap seal depth required for this fixture?

  1. 1 inch
  2. 4 inches
  3. 2 inches Correct answer.
  4. 3 inches

Explanation

The code requires a liquid trap seal of at least 2 inches and not more than 4 inches in depth for plumbing fixtures. Floor drains in areas with infrequent use also require trap primers to maintain the seal.

Question 17Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A horizontal wet vent is used to vent a bathroom group consisting of a water closet, a lavatory, and a bathtub. Which condition must be satisfied for the wet vent to be permitted?

  1. The fixtures must be individually vented in addition to the wet vent
  2. The wet vent must be at least 2 inches in diameter for the entire length Correct answer.
  3. The wet vent must be installed with a slope of 1/2 inch per foot
  4. The water closet must connect downstream of the other fixtures

Explanation

A horizontal wet vent must be sized at least 2 inches and must be a dry vent at its upstream end. The water closet typically connects downstream so that its discharge does not siphon the other traps.

Question 18Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A new water main is installed in a public right-of-way. What is the minimum required separation between the water main and a parallel sanitary sewer line under the code?

  1. 2 feet horizontally and 6 inches vertically
  2. No separation is required if both pipes are pressure tested
  3. 10 feet horizontally and 18 inches vertically Correct answer.
  4. 5 feet horizontally and 1 foot vertically

Explanation

The code requires a horizontal separation of at least 10 feet between water mains and parallel sanitary sewers, and where they cross, the water main must be at least 18 inches above the sewer. These distances reduce the risk of contamination from leakage.

Question 19Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing inspector finds a fixture drain connected to a vent that also serves as a drain for another fixture. What is the most likely code violation?

  1. The vent is undersized for the fixture
  2. The vent is being used as a combination waste and vent without meeting the requirements Correct answer.
  3. The fixture drain lacks a trap
  4. The vent terminates below the roof line

Explanation

A pipe serving as both a drain and a vent must meet the specific combination waste and vent provisions, which impose limits on fixture types, sizing, and slope. Using a drain as a vent without meeting those conditions is a violation.

Question 20Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A 3-inch horizontal drainage pipe carries a branch with a change of direction of 90 degrees from horizontal to vertical. Which fitting is required at the transition?

  1. A short-turn quarter bend
  2. A long-turn quarter bend or a combination wye and eighth bend Correct answer.
  3. A double sanitary tee
  4. A sanitary tee

Explanation

Where a horizontal drain changes to vertical, the code requires a long-turn fitting or a combination wye and eighth bend to keep solids moving and prevent clogging. Short-turn fittings are not permitted at that transition.

Question 21Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

An existing building is undergoing a change of occupancy from a warehouse to a restaurant. What does the code require regarding the plumbing system?

  1. The plumbing system must be evaluated and brought into compliance for the new occupancy's fixture requirements Correct answer.
  2. The building must be demolished and rebuilt
  3. Only the kitchen plumbing must be upgraded
  4. The plumbing system may remain unchanged if it was code-compliant when installed

Explanation

A change of occupancy triggers a review of the plumbing system against the requirements for the new use, including fixture counts, accessibility, and backflow protection. The system must be upgraded where it does not meet current requirements for the new occupancy.

Question 22Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A grease interceptor is required for a restaurant's kitchen drainage. Which installation practice is consistent with the code?

  1. Installing the interceptor on the building sewer downstream of all fixtures
  2. Burying the interceptor with no access for maintenance
  3. Connecting the interceptor to a fixture drain without a vent
  4. Installing the interceptor as close as practical to the fixtures it serves and venting it properly Correct answer.

Explanation

Grease interceptors must be located close to the fixtures they serve, be accessible for cleaning, and be vented to prevent trap seal loss and odors. Proper venting and access are essential to maintain performance.

Question 23Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building's water distribution system serves a fixture requiring a minimum pressure of 8 psi. The available pressure at the water main is 55 psi, and friction loss through the service and distribution piping is calculated at 40 psi. What conclusion follows under the code's pressure requirements?

  1. The system is inadequate because the residual pressure at the fixture is below the minimum Correct answer.
  2. The system requires a booster pump only if the fixture is a flushometer valve
  3. The system is adequate because friction loss is not considered
  4. The system is adequate because 55 psi exceeds the fixture requirement

Explanation

Residual pressure at the fixture equals available main pressure minus friction and elevation losses. Here 55 psi minus 40 psi leaves 15 psi, which is above 8 psi, so the fixture minimum is met; the correct analysis requires checking the residual, not the main pressure alone.

Question 24Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing system is installed with a water-distribution pipe passing through a foundation wall below grade. Which protection is required where the pipe passes through the wall?

  1. A cleanout at the wall penetration
  2. Direct embedment in concrete with no sleeve
  3. A flexible coupling on each side of the wall
  4. A sleeve or annular space sealed to prevent the entry of water and gases Correct answer.

Explanation

Pipe penetrations through foundation walls below grade must be protected with a sleeve or sealed annular space to prevent water and soil gas from entering the building. This also protects the pipe from differential movement and corrosion.

Question 25Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing fixture is installed in a commercial building and must comply with accessibility standards. What is the required height of the lavatory rim above the finished floor?

  1. 42 inches maximum
  2. 36 inches maximum
  3. 34 inches maximum Correct answer.
  4. 30 inches maximum

Explanation

Accessible lavatories must be installed with the rim at a maximum of 34 inches above the finished floor, with knee and toe clearance provided below. This height accommodates a person using a wheelchair.

Question 26Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

Under the DC Plumbing Code, what is the maximum allowable length of a lavatory trap arm when the trap arm is 1-1/4 inches in diameter?

  1. 5 feet Correct answer.
  2. 8 feet
  3. 3 feet
  4. 6 feet

Explanation

The DC Plumbing Code, based on the International Plumbing Code, limits the trap arm length based on the pipe diameter to ensure proper venting and to prevent self-siphonage. For a 1-1/4-inch trap arm, the maximum developed length from the trap weir to the vent fitting is 5 feet. This length corresponds to the critical distance where the trap arm slope of 1/4 inch per foot provides sufficient air space.

Question 27Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the minimum required size of a building sewer serving a single-family dwelling with four water closets and various other fixtures?

  1. 6 inches
  2. 3 inches
  3. 2 inches
  4. 4 inches Correct answer.

Explanation

The DC Plumbing Code requires that the building sewer be sized based on the total drainage fixture units (dfu) served. For a single-family dwelling with four water closets, the total dfu typically exceeds 20, which mandates a minimum 4-inch building sewer. A 3-inch sewer is limited to a maximum of 20 dfu for a building sewer, and a 2-inch sewer is only allowed for certain limited fixtures.

Question 28Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

When a water heater is installed in a location where the relief valve discharge pipe could be subjected to freezing, what is the minimum requirement for the discharge pipe termination?

  1. Terminate at least 12 inches above the floor.
  2. Terminate at least 12 inches above grade outside the building.
  3. Terminate at least 6 inches above grade outside the building. Correct answer.
  4. Terminate at least 6 inches above the floor.

Explanation

The DC Plumbing Code requires that the discharge pipe from a temperature and pressure relief valve terminate not more than 6 inches above the floor or outside the building not more than 6 inches above grade. When freezing is a concern, terminating outside above grade is permitted, but the pipe must be protected from freezing. The code specifies that the termination point must be at least 6 inches above grade when discharged outdoors.

Question 29Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the minimum size of a vent stack required to vent a 4-inch building drain?

  1. 3 inches Correct answer.
  2. 4 inches
  3. 1-1/2 inches
  4. 2 inches

Explanation

The DC Plumbing Code requires that a vent stack be sized according to the drainage fixture units connected and the developed length of the vent. For a 4-inch building drain, the vent stack must be at least 3 inches in diameter to provide adequate venting and to prevent pressure fluctuations. This minimum size ensures that the vent can handle the air displacement from the larger drain.

Question 30Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

Under the DC Plumbing Code, what is the minimum required diameter of a water service pipe for a building with a peak demand of 30 fixture units?

  1. 3/4 inch
  2. 1-1/4 inches
  3. 1 inch Correct answer.
  4. 1-1/2 inches

Explanation

The DC Plumbing Code provides a table for sizing water service pipes based on the total fixture units and the available pressure. For a peak demand of 30 fixture units, the minimum required diameter is 1 inch, assuming a typical pressure and length. A 3/4-inch service would be insufficient and could result in inadequate pressure at fixtures.

Question 31Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the minimum required air gap for a fixture with an effective opening of 1 inch when connected to a potable water supply?

  1. 1 inch
  2. 3 inches
  3. 1-1/2 inches
  4. 2 inches Correct answer.

Explanation

The DC Plumbing Code requires an air gap that is at least twice the effective opening of the fixture inlet, but not less than 1 inch. For an effective opening of 1 inch, twice that is 2 inches, so the minimum air gap is 2 inches. This ensures protection against backflow by maintaining a physical separation.

Question 32Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

According to the DC Plumbing Code, what is the minimum required slope for a 3-inch horizontal drainage pipe?

  1. 1/4 inch per foot
  2. 1 inch per foot
  3. 1/2 inch per foot
  4. 1/8 inch per foot Correct answer.

Explanation

The DC Plumbing Code permits a minimum slope of 1/8 inch per foot for horizontal drainage pipes 3 inches in diameter and larger, provided that the pipe carries the required capacity. This reduced slope is allowed to accommodate limited vertical space while still maintaining adequate flow velocity. For pipes smaller than 3 inches, a 1/4 inch per foot slope is typically required.

Question 33Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

What is the minimum required size of a vent pipe for a single lavatory with a 1-1/4-inch drain?

  1. 1-1/2 inches
  2. 1-1/4 inches Correct answer.
  3. 3 inches
  4. 2 inches

Explanation

The DC Plumbing Code requires that a vent pipe be at least one-half the diameter of the drain it serves, but not less than 1-1/4 inches. For a lavatory with a 1-1/4-inch drain, one-half is 5/8 inch, so the minimum vent size is 1-1/4 inches. This ensures adequate venting for the fixture.

Question 34Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing inspector finds that a 4-inch building drain has a slope of 1/8 inch per foot. Is this acceptable under the DC Plumbing Code?

  1. No, because the minimum slope for 4-inch pipe is 1/2 inch per foot.
  2. Yes, because 1/8 inch per foot is the minimum slope for 4-inch pipe. Correct answer.
  3. No, because the minimum slope for 4-inch pipe is 1/4 inch per foot.
  4. Yes, but only if the pipe is not more than 10 feet long.

Explanation

The DC Plumbing Code allows a minimum slope of 1/8 inch per foot for horizontal drainage pipes that are 3 inches in diameter or larger. Therefore, a 4-inch building drain at 1/8 inch per foot is acceptable, provided it meets the capacity requirements. This provision helps accommodate installations where a steeper slope is impractical.

Question 35Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A 3-inch horizontal drainage pipe carries a branch with a change of direction of 90 degrees from horizontal to vertical. What fitting is required at this change of direction?

  1. A short-turn quarter bend
  2. A long-turn quarter bend Correct answer.
  3. A sanitary tee
  4. A wye branch

Explanation

The DC Plumbing Code requires that changes in direction of drainage flow from horizontal to vertical, or vertical to horizontal, be made with fittings that provide smooth flow and minimize clogging. For a 90-degree change from horizontal to vertical, a long-turn quarter bend (or a combination of fittings with equivalent sweep) is required. A sanitary tee is not permitted for this change because it can cause flow restriction.

Question 36Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A water heater is installed in a building's basement without a relief valve discharge pipe routed to a safe location. What does the DC Plumbing Code require for the discharge pipe termination?

  1. Terminate at least 12 inches above the floor.
  2. Terminate at least 12 inches above grade outside the building.
  3. Terminate at least 6 inches above grade outside the building.
  4. Terminate at least 6 inches above the floor. Correct answer.

Explanation

The DC Plumbing Code requires that the discharge pipe from a temperature and pressure relief valve terminate not more than 6 inches above the floor or outside the building not more than 6 inches above grade. When discharged indoors, the pipe must terminate at least 6 inches above the floor to prevent the discharge from being blocked and to allow for safe drainage. This is a critical safety requirement to prevent excessive pressure buildup.

Question 37Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building's water service pipe is 2 inches in diameter and supplies a building with a peak demand of 60 fixture units. What is the minimum required size of the water meter?

  1. 3/4 inch
  2. 1-1/2 inches Correct answer.
  3. 5/8 inch
  4. 1 inch

Explanation

The DC Plumbing Code requires that the water meter be sized based on the peak demand in fixture units and the pressure loss. For a demand of 60 fixture units, a 1-1/2-inch meter is typically the minimum size that can handle the flow without excessive pressure loss. Smaller meters would not provide adequate capacity and could result in insufficient pressure at fixtures.

Question 38Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A vent stack serving a group of fixtures extends through a roof in a region subject to freezing. What is the minimum required height of the vent stack above the roof?

  1. 18 inches
  2. 6 inches
  3. 12 inches Correct answer.
  4. 24 inches

Explanation

The DC Plumbing Code requires that vent stacks extend at least 6 inches above the roof, but in areas subject to freezing, they must extend at least 12 inches above the roof to prevent frost closure. The additional height helps keep the vent opening clear of snow and ice. Therefore, the minimum height in freezing regions is 12 inches.

Question 39Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A floor drain is installed in a public restroom and is not expected to receive regular flow. What is the minimum trap seal depth required?

  1. 2 inches
  2. 6 inches
  3. 4 inches Correct answer.
  4. 3 inches

Explanation

The DC Plumbing Code requires a minimum trap seal depth of 2 inches for most fixtures, but for floor drains that are not expected to receive regular flow, a deeper trap seal of at least 4 inches is required to prevent evaporation and sewer gas entry. This is because the water in the trap can evaporate over time, and a deeper seal provides more protection.

Question 40Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A horizontal wet vent is used to vent a bathroom group consisting of a water closet, a lavatory, and a bathtub. Which condition must be met for the wet vent to be permitted?

  1. The lavatory must be the most downstream fixture. Correct answer.
  2. The wet vent must be sized at least 2 inches in diameter.
  3. The water closet must be the most downstream fixture.
  4. The bathtub must be the most downstream fixture.

Explanation

The DC Plumbing Code permits a horizontal wet vent for a bathroom group if the lavatory is the most downstream fixture on the wet-vented branch. This ensures that the lavatory's trap seal is not subject to pressure fluctuations from other fixtures. The water closet and bathtub must connect upstream of the lavatory drain.

Question 41Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A new water main is installed in a public right-of-way. What is the minimum required separation between the water main and a parallel sanitary sewer main?

  1. 10 feet Correct answer.
  2. 15 feet
  3. 5 feet
  4. 12 feet

Explanation

The DC Plumbing Code requires a minimum horizontal separation of 10 feet between a water main and a parallel sanitary sewer main to protect the potable water supply from contamination. This separation can be reduced if the sewer is constructed with approved materials and the water main is properly protected, but the standard minimum is 10 feet.

Question 42Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing inspector finds a fixture drain connected to a vent that also serves as a drain for another fixture. What is the correct term for this prohibited arrangement?

  1. Wet vent
  2. Combination waste and vent Correct answer.
  3. Cross-connection
  4. Siphonic vent

Explanation

The DC Plumbing Code prohibits a combination waste and vent system for most fixtures because it can allow sewer gas to enter the building and cause trap siphonage. However, the code does allow certain combination waste and vent systems under specific conditions. The term for a pipe serving as both a drain and a vent is a combination waste and vent, and it is generally prohibited except where explicitly permitted.

Question 43Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

An existing building is undergoing a change of occupancy from a warehouse to a restaurant. What does the DC Plumbing Code require regarding the plumbing system?

  1. The plumbing system must be brought into full compliance with the current code for the new occupancy. Correct answer.
  2. The plumbing system must comply with the code for the original occupancy.
  3. Only the fixtures that are replaced must comply with the current code.
  4. The existing plumbing system can remain if it was compliant with the code at the time of original construction.

Explanation

The DC Plumbing Code requires that when a building undergoes a change of occupancy, the plumbing system must be brought into compliance with the requirements for the new occupancy. This ensures that the new use, which may have different fixture requirements and demands, is safe and sanitary. The code does not allow existing systems to remain if they do not meet the current requirements for the new occupancy.

Question 44Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A grease interceptor is required for a restaurant's kitchen drainage. Which installation practice is consistent with the DC Plumbing Code?

  1. Install the interceptor with a trap on the inlet side.
  2. Install the interceptor on the building sewer downstream of all fixtures.
  3. Install the interceptor with a minimum flow rate of 50 gpm.
  4. Install the interceptor with a vent pipe to relieve pressure. Correct answer.

Explanation

The DC Plumbing Code requires that grease interceptors be vented to prevent pressure buildup and to allow for proper operation. The vent must be installed on the outlet side of the interceptor or as specified by the manufacturer. Additionally, the interceptor must be sized according to the flow rate and installed downstream of the fixtures it serves but before other fixtures.

Question 45Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building's water distribution system serves a fixture requiring a minimum pressure of 8 psi. The available pressure at the water meter is 50 psi. What is the maximum allowable pressure loss due to friction and elevation between the meter and the fixture?

  1. 50 psi
  2. 58 psi
  3. 42 psi Correct answer.
  4. 8 psi

Explanation

The maximum allowable pressure loss is the difference between the available pressure at the meter and the minimum required pressure at the fixture. Therefore, 50 psi minus 8 psi equals 42 psi. This means the combined friction loss and elevation loss must not exceed 42 psi to ensure the fixture receives at least 8 psi.

Question 46Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing system is installed with a water-distribution pipe passing through a foundation wall below grade. Which protection is required by the DC Plumbing Code?

  1. The pipe must be installed with a flexible coupling at the wall penetration.
  2. The pipe must be protected against frost action and corrosion. Correct answer.
  3. The pipe must be encased in a sleeve with a minimum 2-inch annular space.
  4. The pipe must be provided with a clearance of at least 12 inches from the wall.

Explanation

The DC Plumbing Code requires that water-distribution pipes passing through foundation walls below grade be protected against frost action and corrosion. This typically involves insulating the pipe and using corrosion-resistant materials or coatings. The code does not mandate a sleeve or specific clearance, but it does require protection from damage.

Question 47Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing fixture is installed in a commercial building and must comply with accessibility standards. What is the required height of a lavatory rim above the finished floor?

  1. 42 inches maximum
  2. 36 inches maximum
  3. 30 inches maximum
  4. 34 inches maximum Correct answer.

Explanation

The DC Plumbing Code, referencing ICC A117.1, requires that accessible lavatories have a rim height not exceeding 34 inches above the finished floor. This allows wheelchair users to reach the fixture comfortably. A height of 30 inches is typical for standard lavatories but not the maximum for accessibility.

Question 48Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A 6-inch horizontal drainage pipe is installed with a slope of 1/16 inch per foot. Is this acceptable under the DC Plumbing Code?

  1. Yes, because 1/16 inch per foot is allowed for 6-inch pipe. Correct answer.
  2. Yes, but only if the pipe is not more than 20 feet long.
  3. No, because the minimum slope for 6-inch pipe is 1/8 inch per foot.
  4. No, because the minimum slope for 6-inch pipe is 1/4 inch per foot.

Explanation

The DC Plumbing Code allows a minimum slope of 1/8 inch per foot for horizontal drainage pipes 3 inches and larger, but for pipes 6 inches and larger, a slope of 1/16 inch per foot is permitted. Therefore, a 6-inch pipe at 1/16 inch per foot is acceptable. The code provides this allowance for larger pipes to accommodate site conditions.

Question 49Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A building has a 4-inch water service pipe and a 6-inch building sewer. What is the minimum required horizontal separation between these two parallel pipes?

  1. 5 feet
  2. 15 feet
  3. 10 feet Correct answer.
  4. 12 feet

Explanation

The DC Plumbing Code requires a minimum horizontal separation of 10 feet between a water service pipe and a building sewer that are installed parallel. This separation is necessary to protect the potable water supply from contamination. If the 10-foot separation cannot be achieved, the sewer must be constructed with approved materials and the water line must be properly protected, but the standard minimum is 10 feet.

Question 50Plumbing Code and Regulations (DC Plumbing Code, adopted model code, and amendments)

A plumbing system uses a combination waste and vent system for a commercial sink. Which condition must be met for this system to be permitted?

  1. The sink must be located within 5 feet of the vent stack.
  2. The system must be approved by the code official. Correct answer.
  3. The sink must be the only fixture on the system.
  4. The vent must be sized at least 2 inches in diameter.

Explanation

The DC Plumbing Code permits combination waste and vent systems only where specifically approved by the code official. These systems are allowed for certain fixtures, such as commercial sinks, but require approval to ensure they are designed and installed properly. The code does not limit the system to a single fixture or mandate a specific vent size or distance.