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What is a Dishwasher Air Gap?

What is a Dishwasher Air Gap?

If your plumber insists on installing an air gap with your new dishwasher, you might be curious about its purpose. What is this small device protruding above your countertop, and is it truly necessary to protect your dishwasher from contamination?

The truth is that a dishwasher air gap is a cylindrical fitting that links the kitchen sink drain to your dishwasher, preventing the flow of dirty water into and out of the dishwasher during a wash cycle. 

Since the dishwasher empties water directly into your kitchen plumbing, the dishwasher air gap prevents any contaminated dishwater from flowing back into the appliance. 

Keep reading to discover more about dishwasher air gaps and their functionality.

What is its purpose? 

As your dishwasher handles all the dirty dishware by using the best dishwasher detergents, such as Finish, the air gap serves the purpose of diverting wastewater away from the appliance, guaranteeing dishwasher hygiene and thorough cleaning.  

Because dirty water can re-enter the dishwasher, a risk known as backflow, the dishwasher air gap acts as a barrier against this backflow, safeguarding the dishes. 

The air gap efficiently directs the used water away from the dishwasher, channeling it through the drain hose and into the garbage disposal, thereby preventing any backflow.

How it works? 

Dishwasher air gaps create a gap of unpressurized air between two hose branches, which prevents cross-contamination between the dishwasher and the drain.

One branch of the air gap fitting links to the dishwasher, while the other connects and descends toward the garbage disposal. The dishwasher pumps out dirty water through the hose into the air gap, from where it is discharged to the drainage system via the second branch of tubing.

Is it necessary? 

The answer to this question is, “Yes,” you do need an air gap in your dishwasher. It protects your application from contamination by dirty water entering or leaving the drain. 

If your drain hose is connected to the house plumbing at a height lower than 20 inches above the subfloor or floor level, an air gap is required.

Another method to prevent dirty water from entering your dishwasher is by routing the drain hose beneath the counter, maintaining the same elevation as a full sink of water. 

This counteracts the force of gravity, preventing water from the sink from flowing into the dishwasher.


Generally, water shouldn’t come out of the dishwasher air gap. If it is happening, then it signals a problem that requires attention and resolution.

The air gap is a chrome-plated cylinder located on the back of the sink where the faucet is located.

To unclog your dishwasher air gap, start by taking off the cover and utilizing a long-handled bottle brush to eliminate any food particles lodged in the tubing. Another method is to place a paper towel tube over the opening and blow into it to dislodge the debris causing the clog.