Master Plumber Exam DWV and Storm Drainage 2 — Questions and Answers
Question 1: What is the minimum slope required for a 3-inch horizontal drain pipe under the IPC?
- 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 pipe requires a minimum slope of 1/8 inch per foot (1% grade) per IPC Table 704.1.
Question 2: Which type of trap is prohibited by most plumbing codes in the United States?
- P-trap
- Drum trap
- Bottle trap (Correct answer)
- Running trap
Correct answer: Bottle trap
Bottle traps are prohibited because their internal design traps debris and they cannot be properly cleaned or maintained.
Question 3: A combination waste and vent system is permitted for which fixture type?
- Water closets
- Floor drains and sinks (Correct answer)
- Bathtubs
- Showers only
Correct answer: Floor drains and sinks
Combination waste and vent systems are typically permitted for floor drains and sinks where conventional venting is impractical.
Question 4: What is the maximum vertical distance a fixture drain may drop before connecting to a horizontal branch?
- 12 inches
- 18 inches
- 24 inches (Correct answer)
- There is no limit
Correct answer: 24 inches
The IPC limits the vertical drop of a fixture drain to 24 inches before it connects to a horizontal branch drain to prevent siphonage.
Question 5: Storm water from a roof drain must be discharged to which of the following?
- The sanitary sewer system
- An approved storm drainage system or point of disposal (Correct answer)
- The nearest dry well only
- A municipal water main
Correct answer: An approved storm drainage system or point of disposal
Storm water must be discharged to an approved storm drainage system, on-site disposal system, or other approved point — never directly into the sanitary sewer unless permitted by the AHJ.
Question 6: What does the term 'critical level' refer to on an air admittance valve (AAV)?
- The minimum pipe diameter the AAV can serve
- The minimum installation height above the trap weir (Correct answer)
- The maximum pressure differential the AAV can withstand
- The flood level rim of the highest fixture served
Correct answer: The minimum installation height above the trap weir
The critical level (CL) mark on an AAV indicates the minimum height above the trap weir at which it must be installed to function correctly.
Question 7: Which material is NOT generally approved for underground DWV piping?
- ABS
- PVC Schedule 40
- Cast iron
- CPVC (Correct answer)
Correct answer: CPVC
CPVC is a hot-water supply pipe material and is not approved for DWV use; ABS, PVC, and cast iron are all listed DWV materials.
Master Plumber Exam DWV and Storm Drainage 2
What is the minimum slope required for a 3-inch horizontal drain pipe under the IPC?