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IAPMO PPE practice questions

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Question 1Plumbing Code Knowledge

Under a typical plumbing code, what is the minimum required air gap for a fixture supply faucet opening measured above the flood level rim of the receiving fixture?

  1. The diameter of the drain outlet
  2. One inch or twice the effective opening diameter, whichever is greater Correct answer.
  3. One-half inch regardless of opening size
  4. Three inches for all fixtures

Explanation

The standard air gap rule requires the supply opening to sit at least one inch, or twice the effective opening diameter when that is larger, above the flood level rim. This prevents backflow by siphonage even if the opening is large.

Question 2Plumbing Code Knowledge

A water closet compartment is installed with the fixture set against a wall. What minimum clearance is generally required from the centerline of the water closet to each side wall?

  1. 12 inches
  2. 15 inches Correct answer.
  3. 24 inches
  4. 18 inches

Explanation

Codes commonly require at least 15 inches from the centerline of a water closet to any side wall or partition. This provides usable shoulder and elbow space for the occupant.

Question 3Plumbing Code Knowledge

What is the standard minimum diameter for a building drain serving a single-family dwelling?

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

Explanation

A building drain for a dwelling typically must be at least 3 inches in diameter. Smaller sizes are reserved for individual fixture branches, not the main building drain.

Question 4Plumbing Code Knowledge

A vent pipe that also serves as a drain for a fixture above is classified as which type of vent?

  1. A stack vent
  2. A wet vent Correct answer.
  3. A dry vent
  4. A relief vent

Explanation

A wet vent is a vent that also serves as a drainage pipe for fixtures connected above it. Dry vents carry only air and no drainage.

Question 5Plumbing Code Knowledge

In a drainage system, what does the term 'developed length' refer to?

  1. The distance between two cleanouts
  2. The horizontal distance only
  3. The vertical rise of the stack
  4. The total length measured along the centerline of the pipe including fittings Correct answer.

Explanation

Developed length is measured along the centerline of the pipe and fittings, so it accounts for both horizontal and vertical runs. It is used in slope and vent sizing calculations.

Question 6Plumbing Code Knowledge

What minimum size is commonly required for a fixture trap arm serving a lavatory?

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

Explanation

A lavatory trap arm is typically permitted at 1-1/4 inches, matching the common lavatory drain size. Larger sizes are allowed but not required.

Question 7Plumbing Code Knowledge

What is the primary purpose of a trap primer connected to a floor drain?

  1. To increase drain flow rate
  2. To filter debris from the drain
  3. To maintain the trap seal by replenishing water Correct answer.
  4. To vent the drain line

Explanation

A trap primer supplies a small amount of water to a trap that would otherwise evaporate, keeping the seal intact. A maintained seal prevents sewer gas from entering the building.

Question 8Plumbing Code Knowledge

Which material is commonly approved for underground building sewer pipe because of its resistance to corrosion and root intrusion at joints?

  1. Cast iron with lead joints
  2. PVC Schedule 40 with solvent-welded joints Correct answer.
  3. Copper Type M
  4. Galvanized steel

Explanation

PVC Schedule 40 with solvent-welded joints is widely approved for underground building sewers due to corrosion resistance and tight joints. Solvent welding produces a continuous, root-resistant joint.

Question 9Plumbing Code Knowledge

A horizontal drain 3 inches in diameter is installed at the minimum slope. What is that minimum slope?

  1. 1/16 inch per foot
  2. 1/8 inch per foot Correct answer.
  3. 1/4 inch per foot
  4. 1/2 inch per foot

Explanation

Pipes 3 inches and larger are commonly permitted at a minimum slope of 1/8 inch per foot. Smaller pipes generally require 1/4 inch per foot.

Question 10Plumbing Code Knowledge

A 2-inch horizontal drain branch is installed. What is the minimum slope generally required?

  1. 1/16 inch per foot
  2. 1/4 inch per foot Correct answer.
  3. 1/8 inch per foot
  4. 3/8 inch per foot

Explanation

Drains 2 inches and smaller generally require a minimum slope of 1/4 inch per foot to maintain scouring velocity. The 1/8 inch slope applies to 3-inch and larger pipe.

Question 11Plumbing Code Knowledge

What is the maximum allowable distance, in general, between a fixture trap and its vent for a 2-inch trap arm?

  1. 8 feet
  2. 2 feet
  3. 10 feet
  4. 5 feet Correct answer.

Explanation

The trap arm length is limited so the trap weir stays within the vent's protection; for a 2-inch trap arm the common limit is 5 feet. The limit scales with pipe size.

Question 12Plumbing Code Knowledge

A building has a 4-inch soil stack. What is the minimum required size of the stack vent extension above the highest branch?

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

Explanation

The stack vent extension must be at least the size required by vent sizing for the fixtures served, but never smaller than 1-1/4 inches and typically 2 inches for a dwelling stack. It does not have to match the full stack diameter.

Question 13Plumbing Code Knowledge

A grease interceptor is required for a commercial kitchen sink. Where should it be installed relative to the fixture?

  1. At the building sewer connection only
  2. On the vent line above the sink
  3. Above the fixture to allow gravity return
  4. As close as practical to the fixture and downstream of the fixture outlet Correct answer.

Explanation

A grease interceptor must be located downstream of the fixture outlet and as close as practical so grease does not cool and congeal in the line before reaching it. Placing it far away allows accumulation in the pipe.

Question 14Plumbing Code Knowledge

What is the purpose of a backwater valve in a building drain?

  1. To vent the drainage system
  2. To separate gray water from black water
  3. To prevent sewer backflow from entering the building Correct answer.
  4. To reduce water pressure in the supply system

Explanation

A backwater valve closes automatically when flow reverses, preventing sewage from backing up into the building during surcharge conditions. It is installed on the building drain or branch where backflow is possible.

Question 15Plumbing Code Knowledge

A water heater is installed with a temperature and pressure relief valve. Where must the relief valve discharge terminate?

  1. To a point below the flood level rim of a fixture
  2. Into the building drain with a threaded connection
  3. Directly to a floor drain through a trapped connection
  4. To a location where discharge is visible and cannot cause injury, with no thread on the outlet Correct answer.

Explanation

The T&P relief discharge must terminate in a safe, visible location and the outlet must remain unthreaded so it cannot be capped. This prevents a dangerous pressure buildup if the valve opens.

Question 16Plumbing Code Knowledge

A lavatory is installed with a 1-1/4 inch trap. What is the minimum required trap seal depth?

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

Explanation

Traps generally must maintain a liquid seal of at least 2 inches and not more than 4 inches. The 2-inch minimum prevents sewer gas from passing through the trap.

Question 17Plumbing Code Knowledge

When sizing a water service pipe for a building, which factor most directly determines the required pipe size?

  1. The building's total roof area
  2. The slope of the building drain
  3. The number of cleanouts
  4. The fixture unit demand and available pressure Correct answer.

Explanation

Water service sizing depends on the total demand expressed in fixture units and the pressure available at the source. Pipe size must deliver adequate pressure at the farthest fixtures.

Question 18Plumbing Code Knowledge

A fixture drain connects to a horizontal branch with a horizontal to horizontal change of direction. What fitting is generally required?

  1. A long sweep fitting or a combination wye and eighth bend Correct answer.
  2. A reducing coupling
  3. A sanitary tee
  4. A vent tee

Explanation

Horizontal-to-horizontal drainage direction changes require long-radius fittings such as a long sweep or a combination wye and eighth bend to prevent clogging. A sanitary tee is intended for vertical-to-horizontal transitions.

Question 19Plumbing Code Knowledge

A vent stack terminates through a roof. What minimum height above the roof surface is generally required where the roof is not used for other purposes?

  1. 36 inches
  2. 12 inches
  3. 18 inches
  4. 6 inches Correct answer.

Explanation

Vent terminals typically must extend at least 6 inches above the roof surface, with greater heights required when the roof is used for other purposes or near openings. The basic minimum is 6 inches.

Question 20Plumbing Code Knowledge

A horizontal wet vent is used to vent a bathroom group. Which condition must be satisfied for the wet vent to be acceptable?

  1. The wet vent must be at least 4 inches for any bathroom group
  2. The wet vent must terminate below the fixtures
  3. The wet vent must slope at 1/2 inch per foot
  4. The wet vent must be sized to carry the drainage of all fixtures it serves Correct answer.

Explanation

A wet vent must be sized to serve as both a drain and a vent for the fixtures connected to it, so its diameter must accommodate the drainage load. Undersizing would impair both drainage and venting.

Question 21Plumbing Code Knowledge

A building drain must be provided with cleanouts at specified intervals. For a 4-inch horizontal building drain, what is the commonly required maximum distance between cleanouts?

  1. 75 feet
  2. 150 feet
  3. 50 feet
  4. 100 feet Correct answer.

Explanation

Cleanouts on horizontal building drains are generally required at intervals not exceeding 100 feet for 4-inch and larger pipe. Shorter intervals apply to smaller pipe.

Question 22Plumbing Code Knowledge

A water closet is installed in a public restroom. Which flush valve installation detail is required to prevent backflow through the flush valve?

  1. An air gap or vacuum breaker integral to the flush valve Correct answer.
  2. A trap primer on the fixture
  3. A check valve on the supply line
  4. A backwater valve on the branch

Explanation

Flush valves for water closets must incorporate a vacuum breaker or air gap to prevent backflow into the potable supply. This protects the supply from contamination if pressure drops.

Question 23Plumbing Code Knowledge

A storm drainage system conveys roof runoff. Which statement best describes the required separation between storm and sanitary drainage?

  1. Storm drainage may connect to the sanitary vent stack
  2. Storm and sanitary drainage may be combined where the building drain is oversized
  3. Storm drainage must discharge into the sanitary sewer in all cases
  4. Storm drainage must be conveyed in a separate system and may not connect to the sanitary sewer unless specifically permitted Correct answer.

Explanation

Storm drainage is generally kept separate from sanitary drainage to avoid overloading the sanitary system and treatment processes. Combining them is allowed only where local rules specifically permit it.

Question 24Plumbing Code Knowledge

A grease interceptor serving a commercial kitchen must be sized based on which primary factor?

  1. The number of floor drains in the building
  2. The fixture's flow rate and grease retention capacity Correct answer.
  3. The size of the vent stack
  4. The building's water service diameter

Explanation

Grease interceptor sizing depends on the flow rate from the fixtures served and the required grease retention capacity, often computed from fixture unit ratings. Correct sizing prevents grease from passing through to the sewer.

Question 25Plumbing Code Knowledge

A fixture has a drain outlet smaller than the trap it connects to. What is the general rule about trap size relative to the fixture drain?

  1. The trap must be at least the size of the fixture drain outlet Correct answer.
  2. The trap size is unrelated to the fixture drain
  3. The trap must be exactly one size larger than the fixture drain
  4. The trap may be smaller than the fixture drain

Explanation

A trap must not be smaller than the fixture drain outlet it serves, so the trap does not restrict flow. Oversizing is permitted but undersizing is not.

Question 26Plumbing Code Knowledge

A water distribution system is being designed for a building. Which term describes the pressure that remains at a fixture outlet while water is flowing?

  1. Supply pressure
  2. Working pressure
  3. Residual pressure Correct answer.
  4. Static pressure

Explanation

Residual pressure is the pressure measured at a point in the system while water is actually flowing, so friction losses and elevation changes have already reduced the static reading. Static pressure, by contrast, is measured with no flow. Designers check residual pressure to confirm fixtures will operate properly.

Question 27Plumbing Code Knowledge

A plumbing vent is installed to protect a fixture trap. What is the primary function of that vent?

  1. To increase the velocity of drainage through the trap
  2. To allow the trap to be cleaned without removal
  3. To supply combustion air to gas-fired fixtures
  4. To equalize pressure on both sides of the trap seal Correct answer.

Explanation

A vent connects the drainage system to atmosphere so that pressure changes from flowing waste cannot siphon or blow out the trap seal. Equalizing pressure across the seal keeps the water in the trap. Venting does not exist to speed drainage or clean the trap.

Question 28Plumbing Code Knowledge

Which of the following is classified as a major plumbing fixture for the purpose of determining fixture units?

  1. Water closet Correct answer.
  2. Lavatory
  3. Drinking fountain
  4. Floor drain

Explanation

Water closets carry a high fixture-unit value because of their flush volume and frequency of use, and they are treated as major fixtures in drainage load calculations. Lavatories, drinking fountains, and floor drains are assigned much lower values. Fixture units let dissimilar fixtures be added into one comparable drainage load.

Question 29Plumbing Code Knowledge

A plumbing system uses a reduced-pressure principle backflow preventer. What condition causes this assembly to discharge water from its relief port?

  1. A downstream pressure higher than the supply pressure during normal use
  2. A loss of supply pressure combined with a fouled second check valve Correct answer.
  3. A pressure differential across the first check valve that indicates a fouled check
  4. Normal flow through the assembly at design capacity

Explanation

The relief port opens when the differential across the first check is lost, typically because supply pressure drops while the second check fails to hold. That combination lets downstream water escape rather than back up into the supply. Normal flow and ordinary downstream pressure do not cause discharge.

Question 30Plumbing Code Knowledge

A drainage stack serving a building is being checked for sizing. Which factor most directly governs the required diameter of a vertical soil stack?

  1. The total drainage fixture units discharging into the stack Correct answer.
  2. The number of vent terminals on the roof
  3. The developed length of the building sewer
  4. The static pressure at the lowest fixture

Explanation

Soil stacks are sized from the drainage fixture units they receive, subject to the maximum permitted for each diameter. Sewer length, roof vent count, and static pressure do not size the stack. The stack must also be large enough to limit pressure fluctuations that would disturb trap seals.

Question 31Plumbing Code Knowledge

A horizontal drainage pipe is installed with a slope greater than the minimum. What is the general concern with excessive slope on a horizontal drain?

  1. The trap seal will be reduced by capillary action
  2. Solids may be left behind as liquids drain away too quickly Correct answer.
  3. The pipe will exceed its pressure rating
  4. The vent will become a wet vent

Explanation

When a horizontal drain is pitched too steeply, the liquid can run off faster than the solids, leaving waste stranded in the pipe. Codes therefore set a maximum slope for horizontal drainage in addition to a minimum. Pressure ratings and vent types are unrelated to slope.

Question 32Plumbing Code Knowledge

A cleanout is installed at the base of a drainage stack. What is the main reason a cleanout is required at that location?

  1. To provide access to the stack base where the flow turns into the building drain Correct answer.
  2. To permit the stack to be tested with water
  3. To support the weight of the stack above
  4. To allow the stack to be vented to atmosphere

Explanation

The base of a stack is a common blockage point because flow changes direction there, so a cleanout gives access for rodding. Vents, testing, and structural support are handled by other components. Cleanouts are placed where blockages are likely and where a rod can reach the run.

Question 33Plumbing Code Knowledge

A trap arm connects a fixture trap to its vent. Which condition must be maintained along that trap arm?

  1. It must be installed level or with a slight slope and must not change direction by more than the allowed angle before the vent Correct answer.
  2. It must be installed with a slope of one-half inch per foot and be no longer than 12 inches
  3. It must be installed with a slope of at least one-quarter inch per foot and may turn through any angle
  4. It must rise vertically to the vent without any horizontal run

Explanation

The trap arm must stay essentially level, with only a slight fall permitted, and must not make a horizontal turn exceeding the code limit before it reaches the vent. A steep or heavily turned trap arm can create a siphon that pulls the seal. The vent must be reached before the arm drops below the trap weir.

Question 34Plumbing Code Knowledge

A building's water service is being sized. Which pair of factors most directly sets the required service pipe size?

  1. The pipe material and the water temperature
  2. The meter location and the number of shutoff valves
  3. The number of fixtures and the building height
  4. Total demand in fixture units and the available pressure at the source Correct answer.

Explanation

Service sizing balances the total demand, expressed in fixture units or gallons per minute, against the pressure available at the source after friction and elevation losses. Fixture count alone, material, and valve locations do not determine size. The goal is to deliver adequate residual pressure at the farthest fixtures.

Question 35Plumbing Code Knowledge

A water heater is installed in a building. Which requirement applies to the discharge pipe from its temperature and pressure relief valve?

  1. It must be connected directly to the drainage system with a trap
  2. It must discharge to a point where the outlet is not threaded and can be observed Correct answer.
  3. It must terminate within 6 inches of the floor and be trapped
  4. It must be reduced in size to control discharge velocity

Explanation

The relief valve discharge must terminate in a safe, observable location, and the outlet must not be threaded so that a cap or hose cannot be attached to block it. It must not be trapped, and it must not be reduced below the valve outlet size. These rules keep the valve able to relieve pressure safely.

Question 36Plumbing Code Knowledge

A floor drain in a commercial kitchen is provided with a trap primer. Which statement describes the intended operation?

  1. The primer adds a small amount of water to the trap to maintain the seal Correct answer.
  2. The primer opens the trap to the drain during heavy flow
  3. The primer supplies air to break a siphon
  4. The primer injects a chemical that prevents grease buildup

Explanation

A trap primer delivers a small quantity of water to the floor drain trap on a regular basis, replacing water lost to evaporation. Without that makeup water, the seal can evaporate and allow sewer gas into the building. Primers do not treat grease or break siphons.

Question 37Plumbing Code Knowledge

A horizontal branch drain receives a lavatory and a bathtub. What is the general rule about the size of the branch relative to the largest fixture drain connected to it?

  1. The branch must be exactly the same size as every fixture drain on it
  2. The branch must be at least as large as the largest fixture drain connected to it Correct answer.
  3. The branch must be two sizes larger than the largest fixture drain
  4. The branch may be smaller than the largest fixture drain if slope is increased

Explanation

A drainage branch must never be smaller than the largest fixture drain discharging into it, so that flow is not restricted at the connection. It may be larger than that minimum if the load requires it. Increasing slope does not allow a reduction below the fixture drain size.

Question 38Plumbing Code Knowledge

A fixture is installed in a location that is not readily accessible. Which consideration applies to the trap serving that fixture?

  1. The trap must be of the integral type or otherwise accessible for cleaning Correct answer.
  2. The trap must be a drum trap to increase seal volume
  3. The trap must be omitted and replaced with a vent
  4. The trap may be buried in the floor without access

Explanation

Every trap must be accessible for cleaning and repair, so concealed traps must be of a type that can be reached, such as an integral trap with a removable cover. Burying a trap without access prevents maintenance. Drum traps and trap omission are not acceptable substitutes.

Question 39Plumbing Code Knowledge

A plumbing system includes a sump pit that receives sewage. Which requirement applies to the discharge from a sewage ejector?

  1. It must be vented through the building drain
  2. It must be provided with a check valve on the discharge line Correct answer.
  3. It must discharge into a storm drainage system
  4. It must discharge by gravity only

Explanation

A sewage ejector discharge needs a check valve to prevent sewage from flowing back into the pit when the pump stops. The discharge goes to the sanitary drainage system, not storm drainage. The pit itself must be vented, but the discharge line is not vented through the building drain.

Question 40Plumbing Code Knowledge

A plumbing fixture is installed with a water-supply connection that terminates below the flood-level rim of the fixture. Which protection is generally required?

  1. A trap primer on the fixture drain
  2. A vacuum breaker or other approved backflow device on the connection Correct answer.
  3. An air gap at the fixture rim
  4. A check valve on the drainage outlet

Explanation

When a supply outlet sits below the flood-level rim, backflow protection such as an approved vacuum breaker is needed to prevent fixture contents from being drawn into the supply. An air gap would require the outlet to be above the rim. Drainage check valves and trap primers do not protect the potable supply.

Question 41Plumbing Code Knowledge

A horizontal drainage pipe passes through a wall in a building. Which requirement applies to the penetration where the pipe passes through a fire-resistance-rated assembly?

  1. The pipe must be reduced to 2 inches at the wall
  2. The pipe must be wrapped in insulation at the penetration
  3. The penetration must be left open for expansion
  4. The annular space must be sealed with an approved firestop material Correct answer.

Explanation

Penetrations of fire-resistance-rated walls and floors must be protected with an approved firestop system that maintains the rating of the assembly. Leaving the opening unsealed allows fire and smoke to spread. Insulation and pipe size reduction are not substitutes for firestopping.

Question 42Plumbing Code Knowledge

A plumbing fixture is installed with a slip joint in its trap. What is the maximum distance the trap weir may be located above the fixture outlet?

  1. The trap weir must be below the fixture outlet Correct answer.
  2. The trap weir must be level with the outlet
  3. The trap weir must be at least 12 inches above the outlet
  4. The trap weir may be any distance above the outlet if the trap is vented

Explanation

A trap must be installed so that its weir is below the fixture outlet, allowing waste to drain and preventing the fixture from holding water. The trap seal depth is measured from the weir, so the geometry matters. A vent does not allow the weir to be raised above the outlet.

Question 43Plumbing Code Knowledge

A building is served by a public water main. Which arrangement best describes an acceptable air gap for protecting the potable supply?

  1. The supply outlet ends at least two pipe diameters above the flood-level rim of the receiving fixture Correct answer.
  2. The supply outlet is connected through a hose to the fixture
  3. The supply outlet is submerged in the fixture at all times
  4. The supply outlet is fitted with a screen at the rim

Explanation

An air gap is the unobstructed vertical distance between the supply outlet and the flood-level rim, and it must be at least twice the diameter of the outlet with a minimum absolute distance. Submerged outlets, hose connections, and screens do not provide the required separation. The air gap is the most reliable form of backflow protection.

Question 44Plumbing Code Knowledge

A drainage system is being tested with water. Which statement describes the purpose of the water test?

  1. To verify that joints are tight and the system holds water without leakage Correct answer.
  2. To measure the flow rate through the fixtures
  3. To confirm the vent terminals are open
  4. To check the water pressure at the fixtures

Explanation

The water test fills the system and holds it under a head of water to reveal leaks at joints and connections. Flow measurement, vent verification, and pressure checks are separate tests. A passing water test shows the drainage piping is watertight before it is concealed.

Question 45Plumbing Code Knowledge

A storm drainage system and a sanitary drainage system serve the same building. Which statement describes the required separation?

  1. The two systems must be kept separate and must not be connected Correct answer.
  2. The storm system may discharge into the sanitary building drain
  3. The two systems may be combined downstream of the building
  4. The sanitary system may discharge into the storm system

Explanation

Storm drainage and sanitary drainage must remain separate because storm flow would overload the sanitary system and sanitary waste must be treated. Combining them downstream or cross-connecting either direction violates that separation. Separate systems also keep clean runoff out of the treatment process.

Question 46Plumbing Code Knowledge

A water closet is installed with a flushometer valve. Which condition is necessary for the valve to operate properly?

  1. A vent on the flush valve
  2. A floor drain within 3 feet
  3. Adequate flow pressure at the valve during flush Correct answer.
  4. A trap seal of at least 4 inches

Explanation

Flushometer valves need a minimum flowing pressure to deliver a complete flush, so the supply must be sized to maintain that pressure during use. Trap seal depth, valve venting, and proximity of a floor drain are not operating requirements. Insufficient pressure causes weak or incomplete flushing.

Question 47Plumbing Code Knowledge

A building drain is installed below the basement floor. Which requirement applies to the building drain where it passes under a wall footing?

  1. It must be protected from the load of the footing or the footing must be designed to span the pipe Correct answer.
  2. It must be increased one pipe size under the footing
  3. It must be installed with a cleanout at each side of the footing
  4. It must be vented on both sides of the footing

Explanation

A pipe passing under a footing must not be crushed by the structure above, so the pipe is either protected or the footing is designed to carry the load across the pipe. Increasing size, adding cleanouts, or venting does not address the structural load. The concern is the weight transmitted through the footing.

Question 48Plumbing Code Knowledge

A horizontal drain receives flow from a fixture and passes through a wall to the outside. Which fitting is generally required where the drain changes from horizontal to vertical?

  1. A long-sweep fitting or combination wye and eighth bend Correct answer.
  2. A double sanitary tee
  3. A reducing coupling
  4. A sanitary tee

Explanation

Where drainage changes from horizontal to vertical, a long-sweep fitting or a combination wye and eighth bend is used so waste moves smoothly without a sharp turn that could clog. Sanitary tees are for vertical-to-horizontal changes. Reducing couplings have no role in changing direction.

Question 49Plumbing Code Knowledge

A water distribution system is being laid out with a looped main. What is the principal benefit of looping the main rather than using a single dead-end run?

  1. It eliminates the need for a water meter
  2. It allows smaller fixture drains
  3. It reduces pressure loss and improves flow to fixtures by providing multiple paths Correct answer.
  4. It removes the need for backflow protection

Explanation

A looped main gives water more than one path to reach a point, lowering friction loss and improving residual pressure at fixtures during peak demand. It does not eliminate meters or backflow protection. Fixture drain sizing is a drainage matter unrelated to the supply loop.

Question 50Plumbing Code Knowledge

A vertical vent is installed in a building with a drainage stack. Which statement describes the relationship between the vent stack and the drainage stack?

  1. The vent stack may terminate inside the building if it has a charcoal filter
  2. The vent stack must connect to the drainage stack at every floor
  3. The vent stack must extend to open air and may not be connected to the drainage stack below the highest fixture Correct answer.
  4. The vent stack must be the same diameter as the drainage stack at all points

Explanation

A vent stack runs to open air and serves the lower portion of the drainage stack without being connected to it below the highest fixture, so it does not become a wet vent. It may connect at the top. Interior termination with a filter is not permitted, and vent size is determined by vent load, not matched to the stack.