Home Inspector Test Home Inspector Plumbing DWV Systems 2 — Questions and Answers
Question 1: What is the minimum slope required for a 3-inch horizontal drain pipe per the International Plumbing Code?
- 1/16 inch per foot
- 1/8 inch per foot (Correct answer)
- 1/4 inch per foot
- 1/2 inch per foot
Correct answer: 1/8 inch per foot
A 3-inch horizontal drain requires a minimum slope of 1/8 inch per foot (approximately 1%) to ensure adequate flow.
Question 2: A home inspector observes that a toilet's wax ring seal shows signs of leakage at the floor. Which DWV component is most likely failing?
- The closet flange (Correct answer)
- The trap arm
- The soil stack
- The vent pipe
Correct answer: The closet flange
The closet flange connects the toilet to the drain system and supports the wax ring; flange damage or improper height causes wax ring failure and leakage.
Question 3: Which condition is considered a defect when inspecting a P-trap under a bathroom sink?
- The trap is located within 24 inches of the vent
- The trap outlet is higher than the trap inlet (Correct answer)
- The trap is made of PVC
- The trap has a clean-out plug
Correct answer: The trap outlet is higher than the trap inlet
A P-trap outlet higher than the inlet creates a 'S-trap' condition that allows siphoning and loss of the water seal.
Question 4: What does a gurgling sound from a fixture drain typically indicate in a DWV system?
- High water pressure
- A blocked hot water heater
- Inadequate venting causing negative pressure (Correct answer)
- Oversized drain pipes
Correct answer: Inadequate venting causing negative pressure
Gurgling at drains signals that negative pressure in the drain line is pulling air through the fixture trap, a classic sign of inadequate venting.
Question 5: Which material is NOT acceptable for use as a DWV drain pipe in residential construction under most US codes?
- ABS plastic
- Cast iron
- Galvanized steel (Correct answer)
- PVC Schedule 40
Correct answer: Galvanized steel
Galvanized steel is not approved for DWV drain applications because it corrodes internally and restricts flow; it was once used for supply lines only.
Question 6: An inspector finds a washing machine standpipe that is only 12 inches tall. What is the typical deficiency?
- The standpipe is too close to the wall
- The standpipe is too short to prevent backflow (Correct answer)
- The pipe diameter is too large
- There is no clean-out access
Correct answer: The standpipe is too short to prevent backflow
Standpipes for washing machines must typically be 18–42 inches tall to prevent backflow and overflow onto the floor.
Question 7: What is the primary purpose of a clean-out fitting in a DWV system?
- To allow air into the drain system
- To provide access for clearing blockages (Correct answer)
- To reduce water hammer
- To increase drain velocity
Correct answer: To provide access for clearing blockages
Clean-out fittings provide accessible openings so drain snakes or hydro-jet equipment can be inserted to clear obstructions.
Home Inspector Test Home Inspector Plumbing DWV Systems 2
What is the minimum slope required for a 3-inch horizontal drain pipe per the International Plumbing Code?