Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsEasy
A plumber is installing a fixture trap for a commercial dishwasher in a restaurant. The dishwasher discharges indirectly into a floor sink. What is the minimum size for the trap arm connecting the floor sink to the drainage system?
- A3 inches
- B1 1/2 inches
- C2 inches
- D1 1/4 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inches
Commercial dishwashers, due to their high discharge rates and potential for food waste, typically require a minimum 2-inch trap arm for proper drainage and to prevent clogging, according to plumbing codes.
Why the other options are wrong
- A. While acceptable, 3 inches is usually larger than the minimum required for a commercial dishwasher trap arm.
- B. While common for residential sinks, 1 1/2 inches is generally inadequate for commercial dishwasher discharge.
- D. This size is too small for a commercial dishwasher and would likely lead to frequent clogs.
Commercial Dishwasher Trap Arm Size
The minimum diameter required for the trap arm connecting a commercial dishwasher's indirect waste receptor (like a floor sink) to the building's drainage system.
- Ensures adequate flow for high discharge volumes.
- Prevents clogging from food debris.
- Typically 2 inches or larger, depending on local codes and specific appliance requirements.
Memory trick: Dishwasher flow needs a BIGGER pipe, not just a little sip!