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NBOPE Journeyperson Plumber study materials
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NBOPE Journeyperson Plumber practice questions

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Question 1General Plumbing Knowledge, Tools, and Safety

A plumber is about to solder copper tubing in a basement. Which practice best protects occupants from lead exposure from lead-based solder?

  1. Ventilate the area only after the joint is complete
  2. Use only lead-free solder and flux approved for potable water systems Correct answer.
  3. Wipe the joint with a dry rag instead of flux
  4. Use 50/50 tin-lead solder because it flows at lower temperature

Explanation

Lead-based solder is prohibited on potable water piping; only lead-free solder and approved flux may be used on systems conveying drinking water. Good ventilation is still required for flux fumes, but it does not make leaded solder acceptable.

Question 2General Plumbing Knowledge, Tools, and Safety

Before entering a below-grade pit to repair a sewer line, the plumber should first:

  1. Lower a running gas-powered pump into the pit to clear water
  2. Ask a coworker to shout down periodically from the surface
  3. Test the atmosphere for oxygen and toxic gases and set up confined-space controls Correct answer.
  4. Light a match to check whether methane is present

Explanation

Below-grade pits can accumulate hydrogen sulfide, methane, or low oxygen and are treated as confined spaces. Atmospheric testing and attendant/entry controls must precede entry; a gas-powered pump itself adds carbon monoxide.

Question 3General Plumbing Knowledge, Tools, and Safety

Which tool is designed to ream the inside burr from a cut copper tube before soldering?

  1. A soil pipe cutter
  2. A tubing cutter with a folding reamer blade Correct answer.
  3. A flaring block
  4. A hole saw

Explanation

Reaming removes the internal burr left by the cutter wheel, restoring full bore and allowing proper solder capillary flow. Flaring blocks, soil pipe cutters, and hole saws perform unrelated tasks.

Question 4General Plumbing Knowledge, Tools, and Safety

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

  1. To maintain a water seal in floor drain traps that see little use Correct answer.
  2. To filter debris from the potable supply
  3. To raise water pressure at the fixture outlet
  4. To vent the drainage stack above the roof line

Explanation

Floor drain traps in infrequently used areas can evaporate dry, allowing sewer gas into the building. A trap primer delivers small amounts of water to keep the seal intact.

Question 5General Plumbing Knowledge, Tools, and Safety

A plumber is cutting cast iron soil pipe overhead. Which personal protective equipment is most important to prevent eye injury?

  1. Steel-toe boots
  2. A dust mask
  3. Safety glasses with side shields Correct answer.
  4. Cloth work gloves

Explanation

Overhead cutting produces flying chips and dust that fall toward the face, so eye protection with side shields is essential. Gloves, boots, and respirators protect other areas but not the eyes.

Question 6General Plumbing Knowledge, Tools, and Safety

Which of these is the correct way to store a pressurized acetylene cylinder on a service truck?

  1. Upright and secured so the valve cannot be sheared Correct answer.
  2. Lying flat with the valve cap removed
  3. Laid flat and chocked so it cannot roll
  4. Upright but unstrapped for quick access

Explanation

Acetylene cylinders must be kept upright and secured during transport because the acetone solvent can escape if the cylinder lies down, and a sheared valve can release gas violently.

Question 7General Plumbing Knowledge, Tools, and Safety

A 3/4-inch water service must be joined to a meter yoke using a compression fitting. What is the correct sequence when tightening?

  1. Tighten the nut before inserting the tube into the fitting
  2. Hand-tighten the nut, then snug it with a wrench while holding the fitting body Correct answer.
  3. Apply thread sealant to the ferrule and leave the nut loose
  4. Fully tighten with a pipe wrench until the ferrule collapses

Explanation

Compression fittings seal when the ferrule is compressed against the tube; holding the body prevents twisting the tube while snugging the nut. Overtightening crushes the ferrule and causes leaks.

Question 8General Plumbing Knowledge, Tools, and Safety

A plumber is installing a water heater in a garage. Which practice reduces the risk of ignition of gasoline vapors?

  1. Seal the garage door to keep vapors inside
  2. Elevate an ignition-source appliance or use a flammable-vapor-ignition-resistant model Correct answer.
  3. Remove the draft hood to increase combustion air
  4. Install the heater directly on the floor for stability

Explanation

Gasoline vapors are heavier than air and pool near the floor, so ignition sources in garages must be elevated or protected by a flammable vapor ignition resistant design. Removing the draft hood would also create a serious venting hazard.

Question 9General Plumbing Knowledge, Tools, and Safety

What does a plumbing code require for the developed length of a fixture's trap arm before it connects to a vent?

  1. It may be any length as long as the pipe slopes at 1/8 inch per foot
  2. It must be at least 10 feet to ensure adequate venting
  3. It must be vertical for its entire length
  4. It may not exceed the distance that keeps the trap weir within the vent's ability to protect the seal Correct answer.

Explanation

Trap arm length is limited so the trap seal is not subject to back pressure or self-siphonage; the limit depends on pipe size and is tabulated in code. Longer arms require additional venting.

Question 10General Plumbing Knowledge, Tools, and Safety

A plumber is replacing a lavatory faucet and finds the shutoff valves are seized. What is the safest next step?

  1. Cut the supply lines while water is still flowing
  2. Shut off the building main and drain the affected branch before proceeding Correct answer.
  3. Loosen the supply nut and let water spray into a bucket
  4. Force the angle stop with a longer wrench until it turns

Explanation

Forcing a seized stop can break it and cause uncontrolled flow; shutting the main and draining the branch gives a controlled work area. Cutting live lines or loosening nuts under pressure risks flooding and injury.

Question 11General Plumbing Knowledge, Tools, and Safety

Which grade of pipe is typically required for underground DWV installations where the pipe carries waste by gravity?

  1. Any pipe as long as it is joined with solvent cement
  2. Service-weight or schedule appropriate to the burial depth and load Correct answer.
  3. Pipe with a pressure rating equal to the supply main
  4. Thin-wall drain pipe rated for above-ground use only

Explanation

Buried DWV pipe must carry soil loads and resist corrosion; codes specify the wall thickness or schedule based on depth and loading. Above-ground-only products may crush under backfill.

Question 12General Plumbing Knowledge, Tools, and Safety

What is the function of a backwater valve on a basement floor drain?

  1. To regulate the flow rate to the fixture
  2. To admit air behind a slug of waste
  3. To prevent sewage from reversing into the building during a main-line backup Correct answer.
  4. To trap grease before it enters the drain

Explanation

A backwater valve is a one-way check device that closes when flow reverses, protecting low fixtures from surcharge in the public sewer. It does not vent, meter flow, or separate grease.

Question 13General Plumbing Knowledge, Tools, and Safety

A plumber needs to cut a 4-inch PVC DWV pipe square in a tight ceiling space. Which method best produces a square cut?

  1. Use a ratchet-style plastic pipe shear or a miter box with a fine-tooth saw Correct answer.
  2. Use a wood crosscut saw freehand
  3. Use a hammer and chisel to snap the pipe
  4. Score the pipe with a utility knife and bend it until it breaks

Explanation

A square cut is needed for proper solvent-cement joint fit; plastic shears or a miter box guide the blade. A freehand wood saw or scoring and snapping leaves a ragged, out-of-square end.

Question 14General Plumbing Knowledge, Tools, and Safety

When pressure-testing a new water supply system, what is a common code requirement before the test is accepted?

  1. Hold the specified test pressure for a set duration with no loss of pressure Correct answer.
  2. Fill the system with air only and listen for leaks
  3. Test at half the working pressure for five minutes
  4. Test only the fixtures, not the piping

Explanation

Supply systems are typically hydrostatically tested at a pressure above working pressure and held for a specified time with no drop. Air testing is restricted because of stored-energy hazards.

Question 15General Plumbing Knowledge, Tools, and Safety

A plumber is installing a lavatory and notices the drain tailpiece is too short to reach the trap. What is the correct remedy?

  1. Angle the tailpiece so it reaches diagonally
  2. Use a flexible rubber coupling without clamps
  3. Lower the trap by cutting the cabinet floor
  4. Install an extension tailpiece of the proper length Correct answer.

Explanation

The correct fix is to use an extension tailpiece so the trap arm and seal sit at the proper height and alignment. Angling or improvising connections can break the trap seal and leak.

Question 16General Plumbing Knowledge, Tools, and Safety

A plumber is brazing refrigerant or medical gas copper lines. Why is nitrogen purging used during brazing?

  1. To prevent oxidation scale from forming inside the tube Correct answer.
  2. To cool the joint faster than air
  3. To increase the working pressure of the line
  4. To act as a flux for the filler metal

Explanation

A slow nitrogen purge displaces oxygen so the heated interior does not form oxide scale that can contaminate the system. Nitrogen is inert and does not act as flux or pressure booster.

Question 17General Plumbing Knowledge, Tools, and Safety

A plumber is sizing a water closet branch and must decide between a 3-inch and a 4-inch drain. Which factor most directly governs the minimum drain size for a water closet?

  1. The length of the vent stack above the roof
  2. The number of fixtures on the building sewer
  3. The size of the water supply branch
  4. The fixture's outlet size and the code's fixture drain minimum Correct answer.

Explanation

A water closet drain must be at least the size of the fixture outlet and meet the code minimum for that fixture unit load. Vent height, supply size, and total sewer fixtures do not set the individual drain minimum.

Question 18General Plumbing Knowledge, Tools, and Safety

During a hydrostatic test, a gauge reading slowly drops over an hour but no visible leak is found. Which explanation is most plausible?

  1. Trapped air in the system is compressing or dissolving, or the gauge is faulty Correct answer.
  2. The test pressure was too low to register
  3. The water temperature is irrelevant to pressure
  4. The pipe has absorbed the water into its walls

Explanation

Air pockets compress under pressure and can mask or mimic leaks, and a damaged gauge gives false readings. Purging air and verifying the gauge are standard steps before declaring a failure.

Question 19General Plumbing Knowledge, Tools, and Safety

A plumber is using a propane torch near a wall with exposed foam insulation. What is the best control to prevent a hidden fire?

  1. Use a heat shield and keep a fire watch with an extinguisher during and after hot work Correct answer.
  2. Wet the foam first and proceed without a shield
  3. Work quickly so the foam does not have time to ignite
  4. Rely on the smoke detector to warn of fire

Explanation

Hot-work fires often smolder undetected behind shields or inside walls, so a heat shield plus a fire watch and extinguisher are required controls. Wetting foam does not make it noncombustible, and speed or alarms are not controls.

Question 20General Plumbing Knowledge, Tools, and Safety

A plumber is installing a floor drain in a commercial kitchen and must choose between a standard trap and a grease interceptor. Which condition makes the interceptor the correct choice?

  1. The fixture receives fat, oil, and grease-bearing waste from food preparation Correct answer.
  2. The fixture is the only drain in the building
  3. The fixture drains a condensate line
  4. The fixture is more than 10 feet from the vent

Explanation

Grease interceptors are required where FOG-laden waste is discharged, because grease congeals and blocks the building drain. Distance from a vent, fixture count, and condensate drainage do not by themselves require an interceptor.

Question 21Drainage Systems, Fixtures, and Fittings

A 3-inch horizontal branch drain carries a fixture load of 30 fixture units. Under a typical plumbing code, what is the maximum length of this branch before it must be increased in size or provided with a relief vent?

  1. 6 feet
  2. 15 feet
  3. 25 feet
  4. 10 feet Correct answer.

Explanation

A 3-inch branch carrying 30 fixture units is limited to roughly 10 feet of developed length under standard fixture-unit-to-length tables. Beyond that length, the drain must be upsized or a relief vent added to maintain adequate flow and venting.

Question 22Drainage Systems, Fixtures, and Fittings

In a building drain, what is the primary purpose of a cleanout?

  1. To relieve pressure buildup within the vent stack
  2. To provide access for clearing stoppages in the drain Correct answer.
  3. To separate grease from the waste stream
  4. To meter the flow of wastewater leaving the building

Explanation

A cleanout is an accessible opening installed in a drain line so that a plumber can rod or auger a stoppage. It is required at the building drain, at changes in direction, and at the base of stacks.

Question 23Drainage Systems, Fixtures, and Fittings

A fixture drain connects to a vent. What is the maximum vertical distance a trap arm may fall before the vent connection, measured to protect the trap seal?

  1. Six pipe diameters
  2. One pipe diameter Correct answer.
  3. Two pipe diameters
  4. Four pipe diameters

Explanation

The trap arm is limited to a fall of one pipe diameter between the trap weir and the vent connection. This keeps the arm from becoming a partial drain that siphons the trap seal.

Question 24Drainage Systems, Fixtures, and Fittings

Which type of trap is prohibited because it has a moving part that can fail?

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

Explanation

Bell traps rely on a mechanical bell or moving part to maintain the seal and are prohibited. P-traps with a water seal are the standard acceptable trap design.

Question 25Drainage Systems, Fixtures, and Fittings

A soil stack serving a water closet terminates through the roof. What minimum distance must the vent terminal be from an operable window?

  1. 10 feet Correct answer.
  2. 25 feet
  3. 5 feet
  4. 3 feet

Explanation

Vent terminals must terminate at least 10 feet from operable windows, doors, and air intakes to prevent sewer gas from entering the building. The terminal must also be above the roof line.

Question 26Drainage Systems, Fixtures, and Fittings

What is the function of a backwater valve on a building drain?

  1. To prevent reverse flow of sewage into the building Correct answer.
  2. To reduce the velocity of wastewater
  3. To automatically flush the drain at set intervals
  4. To vent the building drain to atmosphere

Explanation

A backwater valve is a check valve installed to stop sewage from reversing into the building when the public sewer surcharges. It is required where fixtures are below the level of the next upstream manhole.

Question 27Drainage Systems, Fixtures, and Fittings

A horizontal drain changes direction from horizontal to vertical. What fitting should be used to promote smooth flow?

  1. Long-sweep 90-degree bend Correct answer.
  2. Sanitary tee
  3. Vent tee
  4. Double sanitary tee

Explanation

A long-sweep bend provides a gradual change of direction that reduces turbulence and the chance of clogging. Sanitary tees are intended for branch connections, not for a horizontal-to-vertical turn in a drain.

Question 28Drainage Systems, Fixtures, and Fittings

What is the minimum size of a building sewer serving a single dwelling with one water closet?

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

Explanation

The minimum building sewer size for a single dwelling is generally 3 inches, provided the fixture load does not require a larger pipe. A 2-inch sewer is too small for a water closet discharge.

Question 29Drainage Systems, Fixtures, and Fittings

A floor drain is installed in a concrete slab. What is the purpose of the trap primer?

  1. To increase the flow rate through the drain
  2. To keep the floor drain trap seal from evaporating Correct answer.
  3. To prevent debris from entering the drain
  4. To vent the floor drain to the stack

Explanation

A trap primer supplies a small amount of water to the trap to maintain its seal when the fixture is rarely used. Without it, evaporation can open the trap and allow sewer gas to escape.

Question 30Drainage Systems, Fixtures, and Fittings

What is the maximum distance a water closet may be from its vent, measured along the drain?

  1. Six feet regardless of pipe size
  2. Ten feet regardless of pipe size
  3. Unlimited, because water closets are self-venting
  4. The distance allowed by the trap arm fall limit for its pipe size Correct answer.

Explanation

The water closet is a fixture and its trap arm is governed by the same one-pipe-diameter fall limit used for other traps. The allowable developed length therefore depends on the pipe size and slope.

Question 31Drainage Systems, Fixtures, and Fittings

Which of the following is a correct method of venting a fixture trap?

  1. Circuit vent
  2. Common vent
  3. Crown vent Correct answer.
  4. Individual vent

Explanation

A crown vent is a vent taken from the crown of the trap, which is not permitted because it can be blocked by the trap seal. The other options are acceptable venting methods.

Question 32Drainage Systems, Fixtures, and Fittings

What is the purpose of a relief vent on a soil stack?

  1. To supply fresh air to the building
  2. To provide a cleanout access point
  3. To relieve pressure fluctuations in the drainage system Correct answer.
  4. To drain condensate from the stack

Explanation

A relief vent relieves pressure changes in the drainage system that could siphon trap seals. It connects the stack to the vent system to equalize pressure.

Question 33Drainage Systems, Fixtures, and Fittings

A horizontal branch drain is installed at a slope of 1/8 inch per foot. What pipe size is typically required to maintain self-cleaning velocity?

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

Explanation

At a slope of 1/8 inch per foot, a larger pipe (generally 4 inches or more) is needed to maintain adequate velocity. Smaller pipes at this shallow slope will not achieve self-cleaning flow.

Question 34Drainage Systems, Fixtures, and Fittings

What is the minimum slope for a 4-inch horizontal building drain?

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

Explanation

A 4-inch building drain is typically required to slope at least 1/8 inch per foot. Smaller pipes generally require 1/4 inch per foot.

Question 35Drainage Systems, Fixtures, and Fittings

Which fitting is used to connect a fixture drain to a horizontal branch without creating a sharp turn?

  1. Sanitary tee
  2. Wye branch Correct answer.
  3. Test tee
  4. Cleanout tee

Explanation

A wye branch provides a gradual, sweeping connection that promotes smooth flow and reduces clogging. Sanitary tees are for vertical-to-horizontal connections.

Question 36Drainage Systems, Fixtures, and Fittings

What is the purpose of a vent stack in a drainage system?

  1. To provide air circulation and pressure equalization Correct answer.
  2. To carry wastewater away from fixtures
  3. To collect grease and solids
  4. To supply water to fixtures

Explanation

A vent stack provides air to the drainage system, equalizing pressure so trap seals are not siphoned. It does not carry wastewater.

Question 37Drainage Systems, Fixtures, and Fittings

A fixture has a trap with a 2-inch seal. What is the minimum trap seal depth required by most codes?

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

Explanation

Most plumbing codes require a trap seal of at least 2 inches and no more than 4 inches. A 2-inch seal is the minimum.

Question 38Drainage Systems, Fixtures, and Fittings

What is the maximum allowable trap seal depth?

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

Explanation

The trap seal must be at least 2 inches and not more than 4 inches deep. Deeper seals can become foul and are harder to maintain.

Question 39Drainage Systems, Fixtures, and Fittings

Which of the following is an approved method for venting a battery of fixtures?

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

Explanation

Circuit venting is an approved method for venting a battery of fixtures with a single vent line. S-traps, bell traps, and drum traps are prohibited or unsuitable.

Question 40Drainage Systems, Fixtures, and Fittings

What is the minimum size of a vent pipe serving a 4-inch soil stack?

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

Explanation

The vent for a 4-inch soil stack must be at least 1-1/2 inches in diameter, though larger vents may be required based on fixture load.

Question 41Drainage Systems, Fixtures, and Fittings

What is the purpose of a grease interceptor?

  1. To increase water pressure
  2. To trap grease and prevent it from entering the drainage system Correct answer.
  3. To filter potable water
  4. To vent the drainage system

Explanation

A grease interceptor captures fats, oils, and grease before they enter the drainage system, preventing clogs. It is required for commercial kitchens and similar fixtures.

Question 42Drainage Systems, Fixtures, and Fittings

A building has a 4-inch building drain and a 3-inch building sewer. What is the required fitting at the transition?

  1. A reducing coupling with a smooth transition Correct answer.
  2. A sanitary tee
  3. A standard tee
  4. A vent tee

Explanation

The transition from a larger building drain to a smaller building sewer must use a reducing fitting that maintains a smooth flow path. A standard tee would create turbulence and is not suitable.

Question 43Drainage Systems, Fixtures, and Fittings

What is the maximum distance between cleanouts on a horizontal drain?

  1. 150 feet
  2. 200 feet
  3. 100 feet Correct answer.
  4. 50 feet

Explanation

Cleanouts are typically required at intervals not exceeding 100 feet on horizontal drains, and at changes in direction. This ensures the line can be rodded effectively.

Question 44Drainage Systems, Fixtures, and Fittings

Which of the following is a correct statement about a combination waste and vent system?

  1. It uses only a vent stack with no drain
  2. It requires a separate vent for every fixture
  3. It is prohibited in all jurisdictions
  4. It combines the drain and vent into a single pipe for certain fixtures Correct answer.

Explanation

A combination waste and vent system uses a single pipe to serve as both drain and vent for certain fixtures, subject to code limitations. It reduces the number of separate vent lines.

Question 45Drainage Systems, Fixtures, and Fittings

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

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

Explanation

A lavatory fixture drain must be at least 1-1/4 inches in diameter. Larger sizes are permitted but not required.

Question 46Drainage Systems, Fixtures, and Fittings

A plumbing code sets the minimum trap arm length for a fixture. What problem does an excessively short trap arm between the trap weir and the vent create?

  1. The trap arm must be installed at a steeper slope
  2. The vent stack must be increased one nominal size
  3. The fixture drain becomes oversized relative to the trap
  4. The trap seal is siphoned or back-pressured because the vent is too close to the weir Correct answer.

Explanation

The vent connection must be far enough downstream of the trap weir that the developed length of the trap arm provides a cushion between the crown weir and the vent opening. If the vent is set too close, pressure changes in the vent or stack can act directly on the trap seal and cause it to be siphoned or blown out. Codes therefore prescribe a minimum developed length of trap arm for each trap size.

Question 47Drainage Systems, Fixtures, and Fittings

A 3-inch horizontal fixture branch must be joined to a 3-inch vertical stack. Which fitting arrangement provides an approved drainage pattern at this transition?

  1. A vent tee installed in the horizontal position
  2. A wye branch with a 45-degree bend, or a combination wye and eighth bend Correct answer.
  3. A double sanitary tee with both branches on the same level
  4. A sanitary tee with the branch entering the stack at 90 degrees

Explanation

Where a horizontal branch enters a vertical stack, the fitting must direct flow in the direction of drainage without creating an abrupt reversal. A wye plus 45-degree bend, or a combination wye and eighth bend, gives a smooth sweeping turn that meets this requirement. Straight tees and double sanitary tees are limited to specific vertical-to-horizontal uses.

Question 48Drainage Systems, Fixtures, and Fittings

A cleanout is installed at the base of a vertical stack. What is the primary reason the cleanout is placed at the base rather than higher on the stack?

  1. To serve as the trap primer connection for the lowest fixture
  2. To permit the stack to be vented through the cleanout during construction
  3. To provide access to the stack offset and the building drain at the point where blockages most often collect Correct answer.
  4. To allow the stack to be tested with water before the fixtures are set

Explanation

Solids and debris moving down a vertical stack lose velocity and tend to settle where the stack turns into the building drain. A cleanout at the base gives direct rodding access to that transition and to the building drain, which is where the majority of stoppages occur. Cleanouts located higher on the stack cannot reach this critical area.

Question 49Drainage Systems, Fixtures, and Fittings

A 2-inch fixture drain with a 2-inch trap discharges into a horizontal branch. The trap arm runs 5 feet at 1/4 inch per foot. What is the resulting fall along the trap arm, and does it stay within the typical code limit for a 2-inch trap arm?

  1. 1 1/4 inches of fall, which is within the typical limit because the limit is based on pipe diameter only
  2. 1 1/4 inches of fall, which exceeds the typical limit of 1 inch for a 2-inch trap arm Correct answer.
  3. 5/8 inch of fall, which is well within the limit
  4. 2 1/2 inches of fall, which requires upsizing the trap arm to 3 inches

Explanation

Fall equals slope times length: 1/4 inch per foot times 5 feet gives 1 1/4 inches. Typical codes limit the fall of a 2-inch trap arm to one pipe diameter, or about 1 inch, so this arm would exceed the limit and the trap would need to be moved closer to the vent. Exceeding the limit risks the arm becoming a wet vent and the trap losing its seal.

Question 50Drainage Systems, Fixtures, and Fittings

A building drain passes through a foundation wall below the level of the adjacent street. A backwater valve is specified. Which installation detail is essential for the valve to function as intended?

  1. The valve must be installed on the vertical stack above the highest fixture
  2. The valve must be installed downstream of the building sewer cleanout and buried without access
  3. The valve must be installed on the horizontal drain with the flow arrow pointing toward the street and provided with a removable cover for access Correct answer.
  4. The valve must be installed with the flow arrow pointing toward the building and provided with a removable cover for access

Explanation

A backwater valve must be oriented so that normal drainage flow holds the flap open and reverse flow from the public sewer closes it, meaning the flow arrow points in the direction of drainage toward the street. Codes also require an accessible removable cover so the valve can be inspected, cleaned, and repaired. Burying it or reversing the arrow defeats its purpose.