Easily Install a Dishwasher Air Gap under your Countertop

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Last updated: April 7, 2023

The cabinetry underneath the sink faucet houses many plumbing pipes and tubes connected from one place to another. Those kitchens have a garbage disposal, dishwasher, and sink plumbing crisscrossed inside, and I often wonder how those systems work together without interference. 

After all, contamination and backflow can occur if the wrong materials are in place or the components cannot process tons of water pressure. An air gap solves that issue, and learning how to easily install a dishwasher air gap under your countertop is simple. An air gap is a y-shaped device with two drain hose sizes separating the dishwasher and garbage disposal’s contaminated water and sludge from clean water. 

The air gap drain hose also pushes everything down the drain using air and stops the contaminants from one appliance from entering the other appliance. I answer the most common questions about air gaps and explain how to install one. I want you to understand why an air gap is a wise investment. 

Table of Contents

Installing a dishwasher air gap under your countertop

1Analyze the countertop until you find a pre-cut hole. The hole is for dishwasher installation, including air gaps. If it is not visible to you, continue to search until you see a flat disc cover sealing the hole.
2Next, turn your attention to the air gap. Connect the small end, a 5/8-inch inlet drain pipe, to the dishwasher drain hose and secure it with hose clamps. An air gap with dual 5/8 inch inlets is best for two dishwashers. 
3The 7/8-inch outlet drain hose next to it should connect to the garbage disposal unit or primary drain. Always use the garbage disposal over the gutter; I only choose the drain when no garbage disposal gets installed.  

The garbage disposal connection sticks out on the side; remove the metal plug inside the tube if it does not. The drain connection to use is a y-branch piece connecting the sink to the drain. Use another hose clamp to secure the attachment. 
4Push the device through the counter gap cap side first. Remove the flat disc cover and any other covers covering the hole.
5Grab a wrench or ask someone to assist me in holding the air gap in its current spot. The air gap will spin during the tightening phase, making it difficult to tighten without a helping hand. 

Screw the nut to the air gap by hand, and then use the wrench to tighten it. Add the covers on top of the now-installed air gap. I would do a thorough inspection to ensure everything is secure.  
6Turn the dishwasher on and run it on a fill cycle. Check this time for water leaks on the disposal, drain, dishwasher, air gap, or cabinet

What size hole do I need for a dishwasher air gap

So, you searched everywhere with no luck in finding the location. Make one yourself. Grab some measuring tape and measure a circumference between .75 and 1.375.  

Draw the smallest hole and see if the air gap will fit through it. If it doesn’t, draw a wider hole. Please continue to make a wider hole within that range until the air gap slides through it. 

Get some masking tape and tape around the hole. That will prevent scratches on the counter. Then, grab a power drill with a hole saw attachment and drill through the countertop

The last step is removing the masking tape and removing dust, and debris. I would reach out to a handyperson for granite and marble countertops, as the material is tough to drill through. 

schematic of a dishwasher air gap installed

How much does an air gap installation cost

Buying it at a home improvement store is worth between $5 and $35. Self-installation only costs much of your time; most materials (wrench, power drill, etc.) are tools you may have. Read the installation manual for the garbage disposal, dishwasher, and air gap before doing this. 

Should you hire a plumber or handyperson for air gap installation, the $5 to $35 air gap goes under materials, not the total price. Labor and per-hour time are other things to pay. Therefore, air gap installation costs for everything are between $50 and $270, including a warranty and not including taxes. 

Does a dishwasher drain need an air gap

It depends on state and local law. I would read the state’s plumbing code, local laws, and sink installation requirements before deciding if an air gap is mandatory. If it is essential, I would install an air gap myself or hire an expert.  

Home sellers will learn the hard way about air gaps when they must install them before it enters the market. A realtor or agent selling a home with no air gaps in a state requiring it is illegal.  

Do new dishwashers have built-in air gaps

Not all new dishwashers have built-in air gaps. Yet, the built-in air gap offers no guarantee it will meet state and local law. Some dishwashers provide a high drain hose loop or standpipe instead of an air gap, hence the concern. 

Therefore, it’s crucial to know plumbing and building code requirements. All obligatory requirements prefer an air gap going through the countertop material over alternatives. 

What is the minimum separation for an air gap

Local and state laws require an air gap if house plumbing is less than 20 inches above the floor or subfloor. Gaps 20 inches and above may get away with no air gaps or alternative options because everything is so far apart that there will be no blockage. However, I would follow local and state laws above all else, even if the gaps are above 20 inches. 

Can I use a high loop instead of an air gap

Choosing alternative backflow prevention solutions to an air gap depends on state and local building and plumbing requirements. You can get away with a high loop installation if the state, city, and county codes do not require air gap installation. A high loop connects the dishwasher to the garbage disposal or drains through hoses under the countertop piping. 

Another alternative is a standpipe. This choice is less welcome in most states than a high loop or an air gap, but again, check state and local laws about whether standpipes are welcome as a backflow solution. A standpipe is a vented, 2-inch vertical pipe connected from the dishwasher to the drain; it installs above the p-trap under the kitchen sink

These alternatives are not as good as an air gap because they cannot handle massive amounts of food waste, sewage, and dirty water. That stuff disrupts the drain cycle by placing contaminated waste in the dishwasher. For standpipes, plumbing experts and handypersons find the hidden installation too complicated. 

Is the water supposed to come out of the dishwasher air gap

It is not normal to see water leaking, dripping, or gushing out of the air gap. Ignoring the water leak will lead to water damage around the area. I suggest searching for the source of the leak and examining the problem.  

Turn off the dishwasher and garbage disposal before troubleshooting. Examine the garbage disposal, the drain, the dishwasher, and the air gap pipe for water issues and smells. Common causes of this are a clog, water flow blockage, and a non-removed knockout plug in the garbage disposal.  

For a knockout plug issue, remove the plug. To remove clogs and blockage, remove the air gap cap and the cap underneath. Take out anything you can reach with your hand, and stick a small brush in the opening using an up and down motion to clear the passageway. 

Moreover, a filled garbage disposal can also be an issue, and if so, run the garbage disposal to see if it clears. If the leak persists after troubleshooting, read the manual for solutions. If the problem persists, contact a plumber.  

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