How to install dishwasher air gap under countertop?

After installing a dishwasher it’s crucial to check the proper functionality of the dishwasher. Sometimes the wastewater flows back to the clean water supply because you may have not installed a dishwasher air gap.

Many homeowners are facing this problem. If you’re also facing this problem then a question may cross your mind How to install dishwasher air gap under countertop by your own?

To solve your problem I have explained the whole process of dishwasher air gap installation easily. Read the whole guide and do it according to the instructions to have a perfect installation.

What is a dishwasher air gap?

In simple words, A dishwasher air gap is a device used to prevent wastewater from a dishwasher from flowing back into the clean water supply. Because this device is installed above the countertop, wastewater cannot flow back into the dishwasher.

Not all dishwasher installations require an above-counter air gap, but the most common way to protect your dishwasher from overflowing with wastewater is the air gap.

How does a dishwasher air gap work?

The air gap separates two branches of the hose from the dishwasher and the drain to the kitchen sink. One connects from the dishwasher and the other one to the kitchen sink using a y-branch tailpiece or garbage disposal.

Because this device is installed above the countertop, wastewater cannot flow back into the dishwasher. When the dishwasher is draining, the waste will discharge through its drain holes to the air gap and exit down the pipe towards the designated drainage site.

How to install dishwasher air gap under countertop?

If you follow this step-by-step guide then I am sure that you can install the dishwasher air gap on your own without the assistance of a plumber.

1. Locate the air gap hole

Find a precut hole specially designed for air gap installation on most of the countertops. It may be hidden with a flat disc cover. Find and remove this disc for air gap installation.

If your countertop does have not a precut hole for air gap installation then, unfortunately, you have to drill it. By using a drill machine, drill a 1-3/8” hole in the countertop near the sink rim for a better drain of overflowed water.

If you are not a professional carpenter then do it with extreme care according to the countertop’s manufacturer’s guides or get the help of a professional carpenter.

2. Connect dishwasher drain hose

The air gap has two legs, one is smaller 5/8″ and the other one is larger 7/8″. The smaller leg for the connection to the dishwasher drain hose. By using a 5/8″ pipe connect the dishwasher drain hose to the 5/8″ air gap leg. Secure the connection tightly by using a hose clamp.

3. Connect garbage disposal

After connecting the air gap to the dishwasher drain hose, it’s time to connect the air gap to the garbage disposal or directly to the drain. Pick a 7/8″ pipe and connect it to the other 7/8” leg of the air gap. Secure the connection tightly with the help of a hose clamp.

If you do have not a garbage disposal then you can directly run the air gap to the drain with the help of a Y-shape tailpiece. Connect the 7/8″ pipe to the Y-shaped tailpiece connecting with the sink and secure it by using a hose clamp.

If you want to install the air gap to the garbage disposal, find a tube on the side of the garbage disposal. If you are installing an air gap first time to the garbage disposal then it will be sealed with a metal plug. Remove it and connect the 7/8″ pipe to the garbage disposal.

4. Secure the air gap on countertop

Remove the flat disc cover from the air gap hole, and insert the air gap device in the hole from below the counter, after removing the vanity cover of the air gap. Screw the mounting nut against the counter to the air gap by hand.

Get some help to assist the nut and tighten the nut by using a wrench. Now add the vanity cover to the top of the newly installed air gap. Now your air gap installation is completed and now it’s time to inspect the working or leakage of the air gap.

5.  Inspection for leaks

Now turn on the dishwasher fill cycle to inspect the working and any leakage. Make sure there is no leakage from the connections because water leakage can cause warping of your cabinets.

If there is no leakage оn thе dіѕроѕаl, drаіn, dіѕhwаѕhеr, аіr gар, оr саbіnеt then congrats you have installed your dishwasher air gap perfectly.

Related post: How To Fix Dull Spot on Quartz Countertop?

Dishwasher Air Gap Alternatives

There are some alternatives to dishwasher air gap if you do not want to install it on the countertop:

High Loop Methode

If you do not want to install a dishwasher air gap then no problem, you can go with the high loop method in which the pipe of the dishwasher runs from the dishwasher to the top of the dishwasher and make a loop by bending it. It prevents the backflow of wastewater.

If you have more than 32 inches of room between the counter and the floor then it will work like an air gap. however, if your room is 32 inches or less then I urge you to install an air gap for proper working.

Check Valve

Installing a check valve in the dishwasher drain line is another alternative to the dishwasher air gap. A check valve is a single-way valve that means when wastewater passed through the valve then it can’t flow back from the valve.


Creating a standpipe is a P-trap is another alternative to the dishwasher air gap to prevent backflow. This involves extending the drain hose and securing it to a vertical pipe or the sink cabinet wall. The height of the standpipe needs to be higher more than 32 inches from the floor to prevent from backflow of wastewater.

How to hide dishwasher air gap?

If the dishwasher air gap is not set better to your countertop then you can hide it by using the following creative ways to ensure it blends in with your kitchen decor.

  • Install the dishwasher air gap under the counter.
  • Place decorative plants or objects on the countertop around the air gap.
  • Install dishwasher air gap near the sink tap.
  • Use air gap alternatives like high loop method, check valve, and standpipe.

Final Thought

Dishwasher air gap installation is an easy process but only if you have a step-by-step guide to do it. According to the need I have written this detailed guide to answer all the questions related to how to install dishwasher air gap under countertop?

I have done my best to cover all the questions related to the dishwasher air gap installation. However, If you have any related question then you can ask us by leaving a comment in the comment section. We will do our best to help you in this regard. Thanks!

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