Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is laying out a new commercial kitchen. An indirect waste receptor is required for a commercial dishwasher. What is the minimum air gap required between the indirect waste pipe and the flood-level rim of the receptor?
- AThe air gap must be at least twice the diameter of the indirect waste pipe, but not less than 1 inch (25 mm).
- B1.5 inches (38 mm)
- C2 inches (50 mm)
- D1 inch (25 mm)
Show answer & explanationAnswer & explanation
Correct answer: A. The air gap must be at least twice the diameter of the indirect waste pipe, but not less than 1 inch (25 mm).
Plumbing codes typically require an air gap for indirect waste receptors to be at least twice the effective diameter of the drain pipe served, but in no case less than 1 inch (25 mm). This ensures protection against back-siphonage and cross-contamination.
Why the other options are wrong
- B. This is a common air gap for other applications but not the specific rule for indirect waste receptors.
- C. This is a common air gap for other applications but not the specific rule for indirect waste receptors.
- D. While 1 inch is a minimum, it doesn't account for varying pipe diameters, making it incomplete.
Indirect Waste Air Gap
A physical separation between the indirect waste pipe and the flood-level rim of the receptor, preventing cross-contamination.
- Crucial for preventing back-siphonage.
- Protects potable water from contamination.
- Calculated based on pipe diameter with a minimum value.
Memory trick: Double the pipe, minimum one, keep the clean water safe, son!