Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsEasy
A plumber is installing a fixture trap for a clothes washer standpipe. What is the minimum trap arm diameter required for this installation?
- A1 1/2 inches
- B1 1/4 inches
- C2 inches
- D3 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inches
Clothes washer standpipes and their traps require a minimum diameter of 2 inches to handle the high volume and flow rate of discharge from a washing machine.
Why the other options are wrong
- A. While common for kitchen sinks, 1 1/2 inches is insufficient for a clothes washer.
- B. This size is typically used for lavatories or single sinks, not clothes washers.
- D. While acceptable, 3 inches is larger than the minimum required for a clothes washer trap arm.
Clothes Washer Trap Arm Size
The minimum diameter for the trap arm serving a clothes washer standpipe to ensure adequate drainage.
- Clothes washer discharge is high volume.
- Requires sufficient diameter to prevent siphoning and clogging.
- Typically 2 inches is the minimum standard.
Memory trick: Washer's Water Needs Wide Way.