Clogged Dishwasher Air Gap: Clean It and Stop Sink Overflow

Water bubbling or spurting out of that small chrome cap beside your faucet is almost never a dishwasher failure. It is a clogged dishwasher air gap, or a clog just past it in the hose that runs to the garbage disposal or sink drain. The fix usually takes 15 minutes with a bottle brush, a towel and a pair of pliers, and it costs nothing.

Here is the short answer. Pull or twist off the decorative cover, unscrew the plastic cap underneath, and pick out food, grease and sludge from the air gap body. Run a thin brush down both openings. Then look under the sink at the larger hose that leads from the air gap to the disposal or drain tailpiece, and clear any blockage there. If you just installed a new disposal, make sure the knockout plug inside its dishwasher inlet was removed, because a plug left in place sends water straight back up through the air gap on the very first cycle.

Once the path is open, run the dishwasher’s drain cycle while watching the counter. A clean air gap stays quiet and dry.

What a Clogged Dishwasher Air Gap Means

An air gap is a backflow prevention device. Dirty dishwasher drain water is pumped up a small hose into the air gap body mounted on the sink or countertop, then falls by gravity through a larger hose into the disposal or a drain fitting. The open space inside the fitting means that if the sink drain ever backs up, contaminated water cannot be siphoned back into the dishwasher. Many local plumbing codes require an air gap, while others accept a high drain loop instead. Check with your local building department if you are unsure what applies in your area.

Because the device is open to the air by design, any blockage downstream has only one place to go: up and out of the vents in the cap. That is why a clog shows up as water on the counter rather than as a dishwasher error.

Signs the Air Gap Is Blocked

• Water spraying, gurgling or dribbling from the cap during the drain portion of a cycle
• Standing water left in the bottom of the dishwasher after the cycle ends
• A sour or rotten smell near the faucet
• Water pooling on the countertop around the air gap base
• Slow draining in the sink that gets worse when the dishwasher runs

A dishwasher air gap leaking only at its base, with no spray from the cap, may instead have a loose mounting nut or a cracked body, which is covered in the troubleshooting section.

Tools and Supplies

• Towels and a small bowl or bucket
• Slip-joint or channel-lock pliers
• Flathead screwdriver
• Long, thin bottle brush or a straightened piece of stiff wire with a bent tip
• Old toothbrush
• Warm water, dish soap and plain white vinegar
• Flashlight
• Replacement hose clamps or a new drain hose, if needed

How to Clean a Dishwasher Air Gap, Step by Step

1. Stop the dishwasher

Cancel the cycle and let the pump stop. Lay a towel around the air gap on the counter, and put a bowl under the sink beneath the hoses in case water drains out when you loosen anything.

2. Remove the decorative cover

Most chrome or colored covers pull straight up. Some twist off counterclockwise. If the cover is stuck, wrap it with a cloth and grip gently with pliers to avoid scratching the finish.

3. Take off the inner cap

Under the cover sits a plastic cap, often with small slots. Twist it counterclockwise to remove it. Pliers help if mineral deposits have locked it in place. You will now see the top of the air gap body with an opening leading down to the hoses.

4. Pick out the clog

This is where the gunk usually sits: bits of food, labels, broken glass, seeds and gray grease sludge. Wear gloves and pull out what you can see. Then work the bottle brush or bent wire down into the body to loosen buildup in the passages. Scrub the cap and cover with an old toothbrush and warm soapy water. Watch for sharp fragments such as broken glass while you work.

5. Flush with water

Pour a cup or two of warm water into the air gap. It should drain quickly. If it backs up, the clog is farther down, in the larger outlet hose or at the disposal inlet.

6. Clear the hose to the disposal or drain

Under the sink, find the larger hose, usually 7/8 inch or so in diameter, running from the air gap to the disposal or drain tailpiece. Loosen the clamp at the disposal end with a screwdriver, pull the hose off over a bowl and inspect it. Flush it with water from the sink sprayer or push a brush through. Then check the disposal’s dishwasher inlet nipple: food can pack into it. Clean it with your finger or a small brush. Never put your hand inside the disposal’s grinding chamber, and make sure the disposal is switched off and unplugged or its breaker is off before reaching anywhere near it.

7. Check for a knockout plug on new disposals

New disposals ship with a plastic plug sealing the dishwasher inlet. Installers are supposed to knock it out with a screwdriver and remove the loose disc from inside the grinding chamber. If your overflow problem began right after a disposal replacement, this is the first thing to check. With power to the disposal off, look into the inlet to confirm it is open.

8. Reassemble and test

Reattach the hose and tighten the clamp snugly. Reinstall the plastic cap and decorative cover. Run the garbage disposal briefly to clear its chamber, then start a short dishwasher cycle or the drain-only function and watch the air gap. A small gurgle is normal. Water escaping from the cap is not.

Troubleshooting a Dishwasher Air Gap Leaking

Water still sprays after cleaning. The blockage may be in the drain itself. If the sink also drains slowly, the clog could sit in the trap or branch line. Clear the trap and, if needed, snake the drain line. A sink drain that cannot keep up will always push water back through the air gap.

Leak at the base on the counter. The mounting nut under the counter may be loose, or the rubber washer may have deteriorated. Tighten the nut from below and replace the washer if it is cracked.

Leak under the sink at the hoses. Old clamps lose tension and rubber hoses harden. Replace clamps and any split or brittle hose sections. Make sure the hose from the dishwasher to the air gap is the smaller one and the hose from the air gap to the drain is the larger one; reversing them causes overflow.

Sagging or kinked outlet hose. The hose from the air gap to the disposal should run downhill without dips. A low loop collects food and grease and clogs repeatedly. Trim it to length and route it with a steady fall.

Recurring clogs every few weeks. Scrape plates well before loading, clean the dishwasher filter monthly, and run the disposal before starting the dishwasher so its inlet is clear. A monthly flush of warm water and a cup of vinegar poured through the air gap helps keep sludge from building up.

Cost Ranges

Cleaning an air gap is free. Replacement hose clamps and a new drain hose cost little at any hardware store. A new air gap fitting generally runs in the range of about $15 to $50 for the part. If you hire a plumber to replace the air gap, clear a deeper drain clog or reroute hoses, expect a service call plus labor that commonly lands somewhere in the low to mid hundreds, depending on your area and what they find.

When to Call a Plumber

Call a licensed plumber if water still backs up after you have cleared the air gap, hose and disposal inlet, because the clog is likely in the branch drain or main line. Bring one in as well if the air gap body is cracked and needs replacement in a stone countertop, if you are changing from an air gap to a high loop and need to confirm what local code allows, or if any drain fitting is leaking inside the cabinet. Electrical work on the disposal circuit belongs to a licensed electrician. For most homes, though, a clogged dishwasher air gap is a quick cleaning job, and a little routine maintenance keeps the counter dry.