Master Plumber Practice Exam

A domestic dishwasher drain must first connect to what?

1. An approved airgap fitting

2. A double-check valve

3. A triple-check valve

4. An approved valve

The correct answer is: An approved airgap fitting

The correct response highlights the importance of using an approved airgap fitting when connecting a domestic dishwasher drain. An airgap is a crucial component in plumbing that serves to prevent potential backflow contamination into the dishwasher. This fitting creates a physical barrier between the dishwasher drain and the home’s wastewater system, ensuring that dirty water cannot siphon back into the appliance. By having an airgap, plumbing systems adhere to health and safety regulations, which are essential for preventing cross-contamination between potable (drinkable) water and wastewater. In many plumbing codes, including those used for residential plumbing, the use of an airgap is mandated for dishwashers to ensure effective functioning and hygiene. Other options, such as double-check and triple-check valves, are important devices for backflow prevention but are not specifically required for the initial connection of a dishwasher drain in typical residential plumbing scenarios. An approved valve alone may not adequately address the risk of backflow, whereas the airgap provides a direct solution to this issue.