Dishwasher Air Gap Leaking? Clean and Reinstall

Why the air gap overflows

The air gap is a small cylinder that sits on the back of your kitchen sink. Its job is to prevent dirty dishwater from siphoning back into your clean water supply. The drain hose from the dishwasher runs up to the air gap, and a second hose runs from the air gap down to the sink drain or disposer. Inside, there is a small vent that lets air into the line, which breaks the siphon.

Water leaks out from under the cap or around the base most often because the internal screen or passageway is clogged. Food scraps and grease build up over time, creating enough resistance that water backs up and finds the easiest exit, which is through the vent or the cap. A loose cap, a cracked body, or hoses that have been pushed off their fittings can also cause leaks, even with a clear passage.

Some municipalities require an air gap by plumbing code, while others allow a high loop in the drain hose. If you have an air gap and it is leaking, it is rarely a sign that the dishwasher itself is broken. The fix is usually a few minutes of cleaning. For a step-by-step on the drain side, see how to clean the drain hose.

Tools and safety basics

You do not need specialized equipment. A flathead screwdriver or a small Allen wrench to remove the cap, an old toothbrush or a narrow bottle brush, a pipe cleaner or a bent wire, and a towel to catch drips are enough. If you plan to disconnect the hoses, you may need pliers to loosen a clamp, but many caps simply pull straight up.

Before you start, turn off the dishwasher and, if possible, leave it off for the rest of the procedure. If you have a continuous feed disposer, make sure it is off as well. Water in the hoses is at room temperature, so there is no burn risk. Work over a small bowl or a cloth to catch residual water that may spill when you remove the cap.

The air gap is a simple mechanical device. There are no electrical components, so the only risk is making a mess. If you are comfortable removing a sink cap, you can handle this.

How to clean the air gap

Start by prying off the decorative chrome or plastic cap. The cap is usually just a friction fit; twist it gently while pulling upward. Once the cap is off, you will see a plastic inner cylinder with a small mesh screen or a narrow slot. This is the primary filter.

Use the toothbrush or bottle brush to scrub the inside of the cylinder and the cap. Pay special attention to the small holes in the mesh. Run the brush back and forth until you can see light through the screen. If there are stubborn bits, use a pipe cleaner or a bent wire to poke them out. Rinse the parts under running water to flush away the debris.

Check the tube that runs from the air gap down to the sink drain. If the air gap was clogged, that tube may also have buildup. You can clean it by running the dishwasher without the air gap cap in place (the water will spray up, so place a cloth over the opening) or by manually feeding a brush down the tube from the top. Reattach the hoses securely after cleaning.

For a detailed walkthrough, see how to install an air gap.

How to reinstall the air gap

If cleaning alone does not stop the leak, the air gap may have shifted or a hose may have come loose. To reinstall, disconnect the two hoses from the air gap. The hoses are usually attached with spring clamps or small screw clamps. Slide each clamp off, then pull the hose straight off the barbed fitting.

Inspect both hoses for cracks, kinks, or blockages. If the hose is split or brittle, replace it with a piece of dishwasher drain hose of the same diameter. Reattach the hoses, pushing them fully onto the barbs until they are snug. Slide the clamps back over the hose and tighten them just enough to hold without crushing the hose.

Set the air gap body back into the sink hole. It should sit flush with the countertop and not rock. If it rocks, you may need to tighten the locknut that holds the body from underneath the sink, or add a small bead of plumber's putty around the base for a watertight seal. Press the cap back on until it clicks or sits firmly.

Run a short rinse cycle or a sink full of water to test. Watch under the sink and around the base for any drips. If the leak is gone, you are done. If it persists, the air gap body itself may be cracked and should be replaced; these are inexpensive parts sold at hardware stores and online, but we do not name any retailer here.

When to consider a new dishwasher

The air gap is a simple fix, but if you find yourself cleaning it multiple times a year, the underlying issue may be a dishwasher that is not draining properly. A partially blocked drain pump, a clogged filter, or a worn drain hose can push water back into the air gap. If your dishwasher is more than eight years old and has required multiple repairs, it may be more cost effective in the long run to replace it.

Modern dishwashers with improved filtration and drain systems are less prone to the kind of debris that clogs an air gap. Small kitchens need every appliance to earn its place, and the same thinking applies when you compare the best air fryers for small spaces. Many also have self-cleaning filters that reduce maintenance. If you decide to replace your dishwasher, consider one that matches your kitchen layout and your washing habits. Built-in models are the most common, but portable and countertop options exist for smaller spaces. Check our guides to compare specs: best built-in dishwashers and budget-friendly dishwasher picks.

A leaking air gap alone does not mean you need a new dishwasher. But if the leak is a symptom of a larger drainage problem, or if the dishwasher is outdated, it might be the right time to upgrade. Look for features like soil sensors and high-efficiency wash systems, which also align with ENERGY STAR criteria for lower water and energy use.

What to do based on your situation

Questions

Is an air gap required by code?

Many local plumbing codes require an air gap for dishwashers, but some allow a high loop instead. Check your local code to see what is required in your area.

Can I remove the air gap entirely?

If your local code allows it, you can replace the air gap with a high loop in the drain hose. However, an air gap provides a physical backflow barrier that is more reliable than a high loop, so keeping it is usually the better choice.

Why does water leak from under the cap even after cleaning?

A leak under the cap after cleaning usually means the cap is not seated properly, the gasket is worn, or the air gap body is cracked. Check the cap and the body for damage, and make sure the cap is pushed down all the way.

How often should I clean the air gap?

With normal use, once a year is enough. If you see water pooling around the cap or hear gurgling from the sink, clean it sooner. In households with heavy food waste, more frequent cleaning may be needed. For more on drain maintenance, see drain air gap cleaning.

Can a leaking air gap damage my countertop?

Yes, if left unchecked, the leaking water can cause staining, warping, or water damage to the countertop and cabinet over time. Fixing the leak quickly is important.

What if the air gap is still leaking after I replace it?

If a new air gap still leaks, the problem is likely elsewhere in the drain line. Check the drain pump and the dishwasher drain hose for clogs or kinks. You may also need to clean the dishwasher filter and the drain path. See our guide on cleaning the drain hose for more help.