Home Inspector Test Home Inspector Plumbing DWV Systems 4 — Questions and Answers
Question 1: What is the minimum diameter of a building drain that receives discharge from a toilet?
- 2 inches
- 3 inches (Correct answer)
- 4 inches
- 6 inches
Correct answer: 3 inches
A toilet (water closet) requires a minimum 3-inch drain to accommodate solid waste without clogging.
Question 2: A home inspector finds that the trap for a floor drain in the basement has no water in it. What hazard does this create?
- Increased risk of drain pipe freezing
- Sewer gases can enter the living space (Correct answer)
- Water hammer in the supply lines
- Reduced drainage capacity
Correct answer: Sewer gases can enter the living space
A dry trap has no water seal to block sewer gases, allowing hydrogen sulfide and methane to enter the building, creating health and safety hazards.
Question 3: Under US plumbing codes, where must a building drain clean-out be located?
- Only at the base of each stack
- Within 100 feet of the building foundation
- Near the connection to the public sewer and at the base of each vertical stack (Correct answer)
- At every horizontal direction change greater than 45 degrees
Correct answer: Near the connection to the public sewer and at the base of each vertical stack
Code typically requires a clean-out near where the building drain exits the foundation and at the base of each soil or waste stack for maintenance access.
Question 4: Which of the following is a sign of a failed or missing trap primer on a floor drain?
- Water backing up from the drain
- Sewer odor in the room with the floor drain (Correct answer)
- Condensation on nearby pipes
- Noisy drain during heavy rain
Correct answer: Sewer odor in the room with the floor drain
A trap primer keeps infrequently used floor drain traps filled with water; without it the trap dries out and sewer gas enters the space.
Question 5: An inspector finds PVC drain pipe installed below the slab without bedding material and resting directly on soil. What is the primary concern?
- PVC is not approved for below-slab use
- Uneven soil settlement can stress joints and cause leaks (Correct answer)
- The pipe diameter is likely too small
- PVC will dissolve in contact with soil
Correct answer: Uneven soil settlement can stress joints and cause leaks
Without proper bedding and backfill, differential soil movement can crack or separate PVC joints, leading to underground leaks that are costly to repair.
Question 6: Which of the following is NOT a function of the DWV system?
- Removing waste and wastewater from fixtures
- Preventing sewer gases from entering the building
- Maintaining water supply pressure (Correct answer)
- Allowing air flow to maintain proper drainage
Correct answer: Maintaining water supply pressure
Water supply pressure is managed by the supply system; the DWV system handles drainage, venting, and waste removal only.
Question 7: A home inspector observes a 'S-trap' under a lavatory. Why is this considered a defect?
- S-traps are too large for lavatory drain openings
- S-traps self-siphon and lose their water seal, allowing sewer gas entry (Correct answer)
- S-traps are only approved for kitchen sinks
- S-traps increase drain noise
Correct answer: S-traps self-siphon and lose their water seal, allowing sewer gas entry
The S-trap's double-curve geometry creates a siphon effect that pulls the water seal out of the trap each time the fixture drains, eliminating the gas barrier.
Home Inspector Test Home Inspector Plumbing DWV Systems 4
What is the minimum diameter of a building drain that receives discharge from a toilet?