Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsEasy
A plumber is installing a P-trap for a kitchen sink. What is the minimum trap seal depth typically required by plumbing codes?
- A1 inch (25 mm)
- B3 inches (75 mm)
- C2 inches (50 mm)
- D4 inches (100 mm)
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inches (50 mm)
Most plumbing codes specify a minimum trap seal depth of 2 inches (50 mm) and a maximum of 4 inches (100 mm) to ensure an effective water seal against sewer gases while allowing for proper drainage.
Why the other options are wrong
- A. 1 inch is generally too shallow and could easily be lost due to evaporation or pressure fluctuations.
- B. 3 inches is within the acceptable range but not the minimum.
- D. 4 inches is the commonly accepted maximum trap seal depth, not the minimum.
Trap Seal Depth
The vertical distance from the crown weir to the dip of a trap, representing the depth of water that forms the seal.
- Prevents sewer gas entry.
- Must be maintained for effective operation.
- Minimum and maximum depths are code-regulated.
Memory trick: A P-trap's seal, a smelly deal, ensures gas won't feel so real!