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Question 1General Requirements, Definitions and Administration

Under a typical plumbing code, which body is generally responsible for adopting the plumbing code and any local amendments that apply within a municipality?

  1. The manufacturer of the plumbing fixtures
  2. The individual licensed plumbing contractor
  3. The local governing authority, such as the city or county council Correct answer.
  4. The property owner of each building

Explanation

Plumbing codes are model documents that become enforceable law only when a governmental jurisdiction formally adopts them, often with local amendments. The governing authority, not private parties, holds this adoption power and also appoints the code official who enforces it. Individual contractors, manufacturers, and owners must comply but cannot adopt or amend the code.

Question 2General Requirements, Definitions and Administration

A plumbing code defines a "fixture unit" primarily as a measure of what?

  1. The physical weight of a fixture in kilograms
  2. The probable peak drainage or supply demand of a fixture relative to a base value Correct answer.
  3. The minimum pipe diameter required by the manufacturer
  4. The number of fixtures allowed on one vent stack

Explanation

A fixture unit is a dimensionless value expressing the probable rate of flow or drainage demand a fixture imposes, relative to a reference fixture such as a lavatory. It allows designers to sum diverse fixtures into a single design load for sizing drainage and water piping. It is not a weight, a vent count, or a manufacturer's diameter requirement.

Question 3General Requirements, Definitions and Administration

A plumbing permit is generally required before installing which of the following?

  1. Cleaning a floor drain with a hand auger
  2. Replacing a faucet aerator on a kitchen sink
  3. Installing a new water heater in a single-family home Correct answer.
  4. Tightening a loose toilet seat bolt

Explanation

Permits are normally required for work that alters or adds plumbing systems, such as installing or replacing a water heater, because inspection verifies safe installation. Routine maintenance and minor repairs that do not change the piping or fixtures typically do not require a permit. Aerator replacement, drain clearing, and tightening a seat bolt are maintenance activities.

Question 4General Requirements, Definitions and Administration

When a plumbing code and a manufacturer's installation instructions conflict, which governs, assuming the manufacturer's instructions are more restrictive?

  1. The plumbing code, because codes always override product literature
  2. The manufacturer's instructions, because the more restrictive requirement controls Correct answer.
  3. The inspecting authority, who must waive both requirements
  4. The building owner, who may choose either document

Explanation

Codes commonly state that where manufacturer instructions impose more stringent requirements than the code, the more restrictive provision governs. This protects the listing and approval of the product, since deviating from instructions can void the listing. The code sets a floor, and stricter product instructions raise that floor.

Question 5General Requirements, Definitions and Administration

In plumbing terminology, what does the term "potable water" mean?

  1. Water that is free of contaminants at levels harmful to health and is suitable for drinking Correct answer.
  2. Water reclaimed from a building's drainage system
  3. Water that has been used once and discharged to a drain
  4. Water stored in a fixture for non-drinking uses

Explanation

Potable water is water that meets health-based quality standards and is safe for human consumption and domestic uses such as cooking and bathing. It is distinguished from gray water, reclaimed water, and drainage, which are not approved for drinking. The definition centers on health safety rather than on prior use.

Question 6General Requirements, Definitions and Administration

A contractor begins plumbing work before obtaining the required permit. What is the typical consequence under plumbing administration provisions?

  1. The work is automatically approved if it passes a later inspection
  2. The owner, not the contractor, bears all penalties in every case
  3. The work is permanently legal because it was completed first
  4. The contractor must obtain the permit and may face fees, penalties, or required removal of concealed work Correct answer.

Explanation

Administrative provisions require a permit before work begins, and starting without one is a violation. The code official may require the permit to be obtained, impose additional fees or penalties, and order that concealed work be exposed for inspection. Completing work first does not create approval.

Question 7General Requirements, Definitions and Administration

What is the primary purpose of requiring inspections at specific stages of plumbing work, such as before concealment?

  1. To transfer liability from the contractor to the inspector
  2. To verify compliance while the work is still visible and correctable Correct answer.
  3. To certify the plumber's license renewal
  4. To increase revenue for the jurisdiction

Explanation

Staged inspections exist so the code official can confirm that piping, joints, and supports comply before they are covered by walls, floors, or concrete. Once concealed, defects are difficult and costly to detect and repair. Inspections are a compliance check, not a revenue tool, liability transfer, or licensing function.

Question 8General Requirements, Definitions and Administration

A code defines a "building drain" as the lowest piping that receives soil and waste from inside the building. Where does the building drain typically terminate?

  1. At the point where it exits the building or connects to the building sewer Correct answer.
  2. At the water service entry
  3. At the roof vent terminal
  4. At the furthest fixture trap

Explanation

The building drain is the lowest horizontal piping inside the building that collects soil and waste and conveys it to the building sewer. It terminates at a point typically one to two feet outside the building wall or at the connection to the sewer. The building sewer then continues to the public sewer or private disposal system.

Question 9General Requirements, Definitions and Administration

Which of the following best describes the role of a plumbing "code official" or authority having jurisdiction?

  1. Interpreting and enforcing the adopted code, including issuing permits and conducting inspections Correct answer.
  2. Setting the prices contractors may charge
  3. Designing the plumbing system for the contractor
  4. Supplying plumbing materials at the job site

Explanation

The code official administers and enforces the adopted plumbing code, which includes reviewing plans, issuing permits, performing inspections, and interpreting code provisions. The official does not design systems, supply materials, or set contractor pricing. Enforcement authority is limited to the code and its administrative provisions.

Question 10General Requirements, Definitions and Administration

A plumber installs a backflow prevention assembly that is listed and approved. Under typical administrative rules, when must the assembly be tested?

  1. At installation and at intervals required by the jurisdiction thereafter Correct answer.
  2. Only when a customer complains about water pressure
  3. Never, because listing guarantees permanent function
  4. Only when the building changes ownership

Explanation

Backflow prevention assemblies are mechanical devices subject to wear, so codes and administrative rules require testing at installation and periodic testing afterward by a qualified tester. Listing certifies the product design but does not guarantee continued field performance. The testing interval is set by the jurisdiction.

Question 11General Requirements, Definitions and Administration

In plumbing code usage, what is the meaning of the term "shall"?

  1. A recommended practice that is optional
  2. A permission granted to the installer
  3. A suggestion for best workmanship
  4. A mandatory requirement that must be complied with Correct answer.

Explanation

Codes use standardized language where "shall" denotes a mandatory requirement, while "should" or "may" indicates a recommendation or permission. This distinction matters in enforcement and in resolving disputes. Treating "shall" as optional would misread the code.

Question 12General Requirements, Definitions and Administration

A homeowner performs plumbing work on a single-family dwelling they occupy. Under many plumbing codes, which statement is generally true about owner-performed work?

  1. Owners are prohibited from ever touching plumbing in their own home
  2. Owners may always perform any plumbing work without permits or inspections
  3. Owners may perform work only if they are licensed contractors
  4. Owners may be allowed to do the work on their own dwelling if they obtain permits and meet inspection requirements Correct answer.

Explanation

Many jurisdictions allow an owner-occupant to perform plumbing work on their own single-family dwelling, but the work still requires permits, must meet code, and is subject to inspection. The allowance is limited to the owner's residence and does not extend to work for others. It is not a blanket exemption from the code.

Question 13General Requirements, Definitions and Administration

Which document typically establishes the minimum requirements for plumbing materials, fixtures, and methods that a local jurisdiction adopts by reference?

  1. The fixture manufacturer's catalog
  2. The building owner's maintenance manual
  3. A model plumbing code published by a standards organization Correct answer.
  4. The contractor's written warranty

Explanation

Model plumbing codes are developed by standards organizations and contain minimum requirements for materials, fixtures, installation, and administration. A jurisdiction adopts a model code by reference, often with amendments, making it enforceable locally. Warranties, catalogs, and maintenance manuals are not codes.

Question 14General Requirements, Definitions and Administration

A contractor installs a water heater and later discovers the relief valve discharge pipe terminates where it could cause injury. Which principle best explains why the code requires correction even though the installation passed rough inspection?

  1. Code compliance is an ongoing obligation, and unsafe conditions must be corrected when discovered Correct answer.
  2. Only the manufacturer can require corrections after inspection
  3. The owner must wait until the next permit cycle to fix it
  4. Inspections are final and cannot be revisited

Explanation

Code compliance is a continuing obligation, and the code official may require correction of violations discovered at any time, including unsafe discharge termination. Passing one inspection does not immunize noncompliant or dangerous conditions. Corrections should be made promptly rather than deferred.

Question 15General Requirements, Definitions and Administration

What is the purpose of requiring plumbing plans or drawings to be submitted for review before issuing a permit for a large commercial project?

  1. To establish the final contract price
  2. To let the code official verify that the design complies with code before construction begins Correct answer.
  3. To replace the need for any field inspections
  4. To allow the contractor to advertise the project

Explanation

Plan review allows the code official to check that the proposed system meets code requirements for sizing, materials, venting, and other provisions before work starts. Catching deficiencies at the design stage avoids costly rework. Plan review supplements but does not replace field inspections.

Question 16General Requirements, Definitions and Administration

A code states that unlisted materials may be used only when approved by the code official based on evidence of compliance with recognized standards. What does this provision primarily accomplish?

  1. It permits alternative materials to be accepted when their suitability is demonstrated Correct answer.
  2. It requires every material to be the most expensive option
  3. It bans all materials that lack a listing
  4. It transfers approval authority to the manufacturer

Explanation

Such provisions create a pathway for alternative or unlisted materials to be accepted when the installer provides evidence, such as test data or engineering evaluation, that the material meets recognized standards. They preserve flexibility while maintaining safety. They do not ban unlisted materials outright or shift approval to manufacturers.

Question 17Plumbing Fixtures, Fixture Fittings and Fixture Requirements

What is the minimum uniform weight a plumbing fixture support must be designed to resist when the fixture rim carries the load?

  1. 300 pounds Correct answer.
  2. 400 pounds
  3. 250 pounds
  4. 150 pounds

Explanation

Fixture supports and the floor or wall attachment must be capable of supporting a 300-pound (135 kg) uniform load applied at the fixture rim, which represents a person standing or sitting on the fixture edge. This requirement protects against failure of the carrier or fastening under realistic use.

Question 18Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A water closet is installed in a public restroom. What is the maximum flush volume allowed for a tank-type water closet under current federal standards?

  1. 0.8 gallons per flush
  2. 1.28 gallons per flush
  3. 3.5 gallons per flush
  4. 1.6 gallons per flush Correct answer.

Explanation

Federal efficiency standards limit tank-type water closets to 1.6 gallons (6 liters) per flush. Older 3.5-gallon models are no longer permitted for new installation, and lower volumes such as 1.28 gallons are common but not the maximum.

Question 19Plumbing Fixtures, Fixture Fittings and Fixture Requirements

Which type of trap is prohibited because it depends on moving parts rather than a water seal to prevent sewer gas passage?

  1. P-trap
  2. Drum trap
  3. S-trap
  4. Bell trap Correct answer.

Explanation

A bell trap relies on a moving or mechanical arrangement rather than a standing water seal, so it can allow sewer gas into the building when the bell is displaced. Codes prohibit bell traps and other non-water-seal traps for plumbing fixtures.

Question 20Plumbing Fixtures, Fixture Fittings and Fixture Requirements

What is the minimum air gap required for a fixture with an effective opening not more than one-half inch in diameter?

  1. Three times the effective opening
  2. One-quarter inch
  3. One inch Correct answer.
  4. One and one-half inches

Explanation

For an effective opening of one-half inch or less, the minimum air gap is one inch. Larger openings require an air gap of at least twice the effective opening, with a minimum of one inch.

Question 21Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A lavatory in a commercial restroom must have a water supply that delivers hot water. What is the minimum temperature the hot water must reach at the fixture?

  1. 120 degrees F
  2. 110 degrees F Correct answer.
  3. 140 degrees F
  4. 100 degrees F

Explanation

Hot water supplied to lavatories and other hand-washing fixtures must reach at least 110 degrees F (43 degrees C) to support proper handwashing. Higher delivery temperatures require tempering devices to prevent scalding.

Question 22Plumbing Fixtures, Fixture Fittings and Fixture Requirements

Which fixture is required to be installed with a water supply that is protected against backflow by an air gap or a vacuum breaker?

  1. A bathtub
  2. A pedestal lavatory
  3. A flushometer water closet
  4. A drinking fountain Correct answer.

Explanation

Drinking fountains and similar fixtures with a submerged or potentially submerged inlet require backflow protection such as an air gap or vacuum breaker. This prevents contamination of the potable supply from the fixture.

Question 23Plumbing Fixtures, Fixture Fittings and Fixture Requirements

What is the minimum size of a fixture drain for a water closet?

  1. One and one-half inches
  2. Two inches
  3. One and one-quarter inches
  4. Three inches Correct answer.

Explanation

A water closet requires a minimum fixture drain of three inches because of the volume and solids it discharges. Smaller drains would be prone to clogging and cannot handle the flush.

Question 24Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A public lavatory is being installed in a restroom. What is the maximum spacing between the lavatory and the nearest wall or partition?

  1. The lavatory must be set at least 15 inches from the wall
  2. There is no maximum spacing requirement Correct answer.
  3. The lavatory must be within 18 inches of the wall
  4. The lavatory must be centered in a 30-inch space

Explanation

The code sets minimum clearances and spacing for lavatories but does not impose a maximum distance from a wall or partition. Designers may locate the fixture anywhere that satisfies the minimum clearances and accessibility requirements.

Question 25Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A floor drain is installed in a food preparation area. What is the minimum size of the fixture drain for a floor drain serving this area?

  1. One and one-half inches
  2. Four inches
  3. Two inches Correct answer.
  4. Three inches

Explanation

Floor drains typically require a minimum fixture drain of two inches to handle the anticipated flow and debris in food preparation and similar areas. Smaller drains are easily clogged and cannot keep up with washdown flows.

Question 26Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture has a continuous waste outlet. What feature must the fixture have to prevent backflow into the potable water supply?

  1. An air gap or backflow preventer Correct answer.
  2. A trap primer
  3. A cleanout
  4. A flush valve

Explanation

Fixtures with a direct or continuous connection to the drainage system must be protected against backsiphonage by an air gap or an approved backflow preventer. This prevents wastewater from being drawn into the potable supply during pressure loss.

Question 27Plumbing Fixtures, Fixture Fittings and Fixture Requirements

What is the minimum required water pressure at a fixture for a flushometer valve to operate properly?

  1. 10 psi
  2. 45 psi
  3. 15 psi Correct answer.
  4. 25 psi

Explanation

Flushometer valves require a minimum flowing pressure of 15 psi to operate correctly and reseat after flushing. Lower pressures can cause the valve to fail to close, wasting water.

Question 28Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A drinking fountain is installed in a public building. What is the maximum height of the fountain's bubbler above the floor?

  1. 48 inches
  2. 36 inches
  3. 42 inches Correct answer.
  4. 30 inches

Explanation

Accessibility standards limit the bubbler outlet of a drinking fountain to a maximum of 42 inches above the floor so that it is reachable from a wheelchair. Lower heights may also be provided in a hi-lo arrangement.

Question 29Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A bathtub has a shower head installed above it. What is the minimum height of the shower head above the floor?

  1. 66 inches
  2. 60 inches
  3. 72 inches Correct answer.
  4. 78 inches

Explanation

Shower heads must be installed at least 72 inches above the floor to provide adequate clearance for users. Higher installation is permitted and is common.

Question 30Plumbing Fixtures, Fixture Fittings and Fixture Requirements

What is the minimum size of a fixture drain for a bathtub?

  1. Three inches
  2. Two inches
  3. One and one-half inches Correct answer.
  4. One and one-quarter inches

Explanation

A bathtub requires a minimum fixture drain of one and one-half inches. This size accommodates the tub's discharge while maintaining adequate flow to the trap.

Question 31Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A water closet is installed in an accessible stall. What is the minimum clear space required in front of the water closet?

  1. 72 inches
  2. 36 inches
  3. 60 inches Correct answer.
  4. 48 inches

Explanation

Accessible water closets require a clear floor space extending at least 60 inches from the wall behind the fixture to allow a wheelchair to approach and transfer. Side clearance of at least 60 inches in width is also typically required.

Question 32Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A lavatory has a rim height of 34 inches. Which requirement does this satisfy?

  1. The maximum rim height for a bathtub
  2. The maximum rim height for an accessible lavatory Correct answer.
  3. The minimum rim height for a standard lavatory
  4. The minimum rim height for a drinking fountain

Explanation

Accessible lavatories must have a rim or counter surface no higher than 34 inches above the floor. This allows a wheelchair user to reach the basin and controls comfortably.

Question 33Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture drain connects to a trap. What is the maximum distance the trap may be located from the fixture?

  1. 12 inches
  2. 36 inches
  3. 30 inches
  4. 24 inches Correct answer.

Explanation

The trap must be located as close as practicable to the fixture, and the developed length of the fixture drain between the fixture and the trap may not exceed 24 inches. Longer distances increase the risk of fouling and trap seal loss.

Question 34Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture is installed with a trap that has a vertical drop on the outlet side before the vent connection. What problem does this create?

  1. It eliminates the need for a vent
  2. It creates an S-trap condition that can siphon the trap seal Correct answer.
  3. It increases the trap seal depth beyond the limit
  4. It increases the fixture drain size

Explanation

A vertical drop immediately after the trap forms an S-trap, which can self-siphon and pull the trap seal out under normal flow. The trap arm must be vented before any vertical drop to preserve the seal.

Question 35Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture has a concealed trap with no accessible cleanout. Why is this installation problematic?

  1. The trap cannot be cleaned or repaired without damaging the building Correct answer.
  2. The trap will not hold a water seal
  3. The trap will exceed the maximum trap arm length
  4. The trap cannot be vented

Explanation

Traps must be accessible for cleaning and repair. A concealed trap without a cleanout or access panel cannot be serviced, which is why codes require access to traps and cleanouts.

Question 36Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A lavatory has a 1.5-inch fixture drain that connects to a 1.5-inch trap arm. The trap arm runs 30 inches to the vent. What is the result?

  1. The installation requires a second vent
  2. The installation requires a larger trap
  3. The installation is acceptable because the drain size is adequate
  4. The installation exceeds the maximum trap arm length for a 1.5-inch trap Correct answer.

Explanation

The maximum developed length of a trap arm depends on its diameter; for a 1.5-inch trap arm the limit is well under 30 inches. Exceeding it risks loss of the trap seal through siphonage, so the vent must be relocated closer.

Question 37Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A water closet is installed in a building where the drainage system is subject to backflow from a combined sewer. What device is required to protect the fixture?

  1. A trap primer
  2. A backwater valve Correct answer.
  3. An air admittance valve
  4. A flushometer valve

Explanation

A backwater valve prevents sewage from reversing into the building drainage system when the public sewer surcharges. It is installed on the building drain or branch serving fixtures subject to backflow.

Question 38Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture has a trap seal that is being lost because the trap is subject to a pressure differential from a nearby stack. What is the most appropriate remedy?

  1. Install a cleanout on the trap
  2. Reduce the fixture drain size
  3. Install a proper vent for the trap Correct answer.
  4. Increase the trap seal depth

Explanation

Trap seal loss from pressure differentials is prevented by venting the trap, which equalizes pressure on both sides of the seal. Increasing seal depth does not address the underlying pressure problem.

Question 39Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture is installed with a direct connection to a drain that also serves as a vent. What is the primary concern?

  1. The fixture will not drain
  2. The fixture drain will be undersized
  3. The fixture may be subject to backsiphonage Correct answer.
  4. The trap will evaporate

Explanation

A direct connection without an air gap or backflow preventer can allow backsiphonage of wastewater into the potable supply or fixture. Proper protection is required to separate the fixture from the drainage system.

Question 40Plumbing Fixtures, Fixture Fittings and Fixture Requirements

A fixture drain serving a single lavatory must connect to a vent. What is the maximum developed length of the trap arm, measured from the trap weir to the vent fitting, for a 1-1/2 inch trap arm?

  1. Six feet Correct answer.
  2. Three feet
  3. Five feet
  4. Eight feet

Explanation

A trap arm must not exceed the distance allowed for its diameter so that the trap weir stays close to the vent and the arm retains a proper slope without becoming self-siphoning. For a 1-1/2 inch trap arm the limit is six feet of developed length from the trap weir to the vent fitting. Longer arms risk loss of trap seal through siphonage.

Question 41Drainage Systems, Traps and Cleanouts

What is the primary purpose of a plumbing trap?

  1. To filter solid waste from the drainage flow
  2. To increase water pressure at the fixture
  3. To measure the volume of wastewater discharged
  4. To prevent sewer gases from entering the building Correct answer.

Explanation

A trap holds a water seal that blocks sewer gas and odors from passing back into the occupied space. The depth of that seal is what makes the trap functional, so its shape and venting must preserve the seal.

Question 42Drainage Systems, Traps and Cleanouts

What is the standard minimum water seal depth for a plumbing trap?

  1. 100 mm
  2. 25 mm
  3. 50 mm Correct answer.
  4. 150 mm

Explanation

A trap must maintain a water seal of at least 50 mm to reliably resist sewer gas. Deeper seals are harder to break by siphonage but increase the risk of fouling and slow drainage.

Question 43Drainage Systems, Traps and Cleanouts

Which fixture trap type is typically required for a bathtub or shower where the drain outlet is in the floor?

  1. Bell trap
  2. Drum trap
  3. P-trap Correct answer.
  4. Bottle trap

Explanation

A P-trap is the common configuration for floor drains and tub/shower wastes because its outlet turns horizontally to connect to the drainage line. It can be installed below the floor with an accessible cleanout.

Question 44Drainage Systems, Traps and Cleanouts

Why must a trap be protected by a vent?

  1. To prevent the water seal from being siphoned out Correct answer.
  2. To reduce the noise of draining water
  3. To allow solid waste to break down faster
  4. To increase the drainage velocity in the branch

Explanation

A vent equalizes pressure on both sides of the trap so that a slug of water flowing down the drain cannot siphon the seal away. Without venting, the trap can lose its seal and allow sewer gas into the building.

Question 45Drainage Systems, Traps and Cleanouts

What does the term "developed length" refer to when sizing a fixture drain?

  1. The distance from the trap to the nearest cleanout
  2. The total length of pipe measured along its centerline including fittings Correct answer.
  3. The vertical distance from fixture to stack
  4. The horizontal run only, excluding vertical drops

Explanation

Developed length is the measured length along the pipe centerline, counting fittings and changes of direction. It is used to determine allowable trap-to-vent distances and pipe sizing because friction increases with length.

Question 46Drainage Systems, Traps and Cleanouts

What is the purpose of a cleanout in a drainage system?

  1. To measure the slope of the drain pipe
  2. To allow air to enter the drainage system
  3. To provide access for clearing blockages in the drain Correct answer.
  4. To collect grease before it reaches the sewer

Explanation

A cleanout gives maintenance personnel access to the inside of the drainage pipe so blockages can be rodded or jetted. It must be accessible and sized to suit the pipe it serves.

Question 47Drainage Systems, Traps and Cleanouts

Which of the following is a common sign that a trap has lost its water seal?

  1. The toilet tank refills constantly
  2. Water draining more slowly than usual
  3. The fixture supply pressure drops
  4. Sewer odor detected near the fixture Correct answer.

Explanation

When the water seal is lost, sewer gas can pass freely into the room, producing a noticeable odor near the fixture. Slow drainage or supply problems point to other causes such as blockage or valve issues.

Question 48Drainage Systems, Traps and Cleanouts

What is the minimum size of a cleanout opening for a drainage pipe of 100 mm diameter?

  1. 50 mm
  2. 75 mm
  3. 40 mm
  4. 100 mm Correct answer.

Explanation

A cleanout should be the same nominal size as the pipe it serves so that cleaning equipment can pass through it. For a 100 mm drain, the cleanout opening should therefore be 100 mm.

Question 49Drainage Systems, Traps and Cleanouts

A fixture drain connects a trap to a vented branch. If the trap arm is too long without a vent, what is the most likely result?

  1. The trap seal may be siphoned out during heavy flow Correct answer.
  2. The fixture will drain too quickly and splash
  3. The vent stack will fill with water
  4. The cleanout will become inaccessible

Explanation

An excessively long trap arm allows a pressure differential to develop during heavy flow, which can siphon the trap seal. Venting within the allowable distance prevents this by admitting air close to the trap.

Question 50Drainage Systems, Traps and Cleanouts

Which condition would most likely cause a trap to lose its seal through evaporation?

  1. A fixture with an oversized supply pipe
  2. A fixture connected to a short vent stack
  3. A fixture that is rarely used, such as a floor drain in an unused room Correct answer.
  4. A fixture with a high flow rate during peak hours

Explanation

Water in a trap slowly evaporates, and with no replenishment the seal can disappear. Floor drains in unused areas are the classic case and often need trap primers to stay sealed.