Journeyman Plumber ExamFixtures, Faucets, and Other AppliancesEasy
A client requests the installation of a new dishwasher. The manufacturer's instructions specify a minimum 7/8-inch air gap for the dishwasher drain hose. Which of the following is the primary reason for installing an air gap?
- ATo provide a convenient point for drain line cleanout.
- BTo ensure proper drainage speed and prevent clogs.
- CTo prevent backflow of contaminated water into the dishwasher.
- DTo comply with aesthetic requirements for countertop fixtures.
Show answer & explanationAnswer & explanation
Correct answer: C. To prevent backflow of contaminated water into the dishwasher.
The primary purpose of an air gap for a dishwasher drain is to prevent contaminated water from the sink or drain system from siphoning back into the dishwasher, which could then contaminate dishes.
Why the other options are wrong
- A. While some air gaps can be opened, their primary design function is not for drain line cleanout.
- B. While proper drainage is important, the air gap's main function is not flow speed or clog prevention.
- D. Aesthetics are not the primary driving factor for plumbing code requirements like air gaps.
Air Gap (Plumbing)
A vertical open space between the lowest part of a water supply outlet and the flood level rim of the fixture or receptacle it discharges into, preventing backflow.
- Essential for cross-connection control.
- Commonly used on dishwashers, RO systems, and indirect wastes.
- Minimum required distance varies by code and application.
Memory trick: Don't let dirty water creep, keep your clean water in the deep.