What Is An Air Gap Dishwasher? | Clean Drain Guide

That short chrome or plastic cap by the faucet is the air gap. One hose comes from the dishwasher; another goes to the drain or disposer. The vented cap breaks any siphon so waste cannot flow back into the machine.

Air Gap Vs High Loop At A Glance

Method	How It Works	Where It Fits
Air gap device	Dishwasher drains to the air gap, then to the sink drain. The vented cap breaks any siphon and blocks backflow.	Often required by local rules; see IPC 802.1.6 and California Plumbing Code §807.3.
High drain loop	The drain hose is looped to the underside of the counter before dropping to the drain. The rise helps reduce backflow.	Allowed by some codes or maker guides when no air gap is mandated. Check your city or state rules and the manual.

How A Dishwasher Air Gap Works

Think of the air gap as a safe break in the line. One hose runs from the dishwasher to the inlet on the side of the device. A second hose runs from the outlet down to the disposer inlet or a branch tailpiece. During a drain cycle, water shoots up to the cap, vents across the gap, and then drops into the outlet hose. Since air sits between the two paths, a blocked sink or disposer cannot pull dirty water back into the tub.

The cap sits above the sink rim so the vent stays dry. If a clog forms, water may splash at the cap where you will spot it fast.

Dishwasher Air Gap Meaning And When To Add One

This device exists to guard the wash from waste and keep drains honest. Many regions call for an air gap on new installs. Some areas allow a high loop when rules permit. If you live in a state that follows the Uniform Plumbing Code, an air gap is common. If your area follows the International Plumbing Code, you may see an air gap or an air break into a receptor. Local code wins, so check before you cut a new hole in the sink.

Even when not required, many pros still fit one. It blocks siphon action better than a loose high loop and makes clogs easy to spot.

Benefits And Tradeoffs

Upsides You Can Count On

• Backflow control that does not rely on a check valve alone.
• Visible warning when the drain path plugs up.
• Stable routing that is not moved by a trash can or by items under the sink.

Possible Downsides

• Needs a hole in the sink deck or counter.
• The cap can look odd next to a single-hole faucet set.
• Food bits can clog the inlet if the disposer knock-out stays in place.

Parts You Will Need

• Listed air gap kit with cap, body, and washers.
• 7/8" drain hose from air gap to disposer or tailpiece.
• 5/8" or maker-specified hose from dishwasher to air gap.
• Two clamps per hose run.
• Branch tailpiece with dishwasher nipple, or a disposer dishwasher inlet.

Install Steps In Plain Words

Prep Before You Start

Unplug the dishwasher or switch off the breaker. Close the stop valves. Clear the sink base so you reach the back wall. Measure hose runs; leave slack for service. Keep a towel and a pan under the work zone to catch drips. If your counter is stone, tape the surface and drill with steady pressure. Wear eye protection when drilling and when knocking out the plug.

1. Pick the spot. The cap must sit above the sink’s flood rim. Keep it near the faucet to save hose length.
2. Drill or punch the hole. Deburr sharp edges so hoses are not cut.
3. Set the body with the gasket, then add washer and nut from below. Hand-tighten, then snug.
4. Run the small hose from the dishwasher to the side inlet. Keep bends gentle.
5. Run the large hose from the outlet to the disposer or tailpiece. Avoid sags.
6. Clamp each end. Tug test to be sure nothing slips.
7. If using a disposer, knock out the plug at the dishwasher inlet and remove the chip.
8. Run a rinse and watch the cap. A small puff is normal. A steady spill means a block downstream.

Position, Height, And Hose Rules

Mount the cap so the flood level mark lines up at or above the sink rim. Keep the outlet hose as short as the layout allows and slope it down to the drain. Place the branch on the sink tailpiece above the trap arm. That prevents sewer gas from reaching the line and keeps the path smooth.

For thick tops, add a support plate under the cap nut. Snug the nut; do not crush the gasket.

Care And Cleaning

Pop the cap off a few times a year. Rinse the insert and brush the slots. Check both hoses for kinks or loose clamps. If the outlet hose feels heavy, pull and rinse it.

Common Problems And Easy Fixes

Water at the cap points to a clog in the outlet hose, branch nipple, or disposer inlet. Pull the hose and clear the path. If the washer will not drain and the cap stays dry, the issue sits between the tub and the inlet. A kinked hose or a stuck check valve near the pump is common. If you added a new disposer and water floods the sink, the knock-out plug may still be in place.

Air Gap Sizes, Adapters, And Sinks

Most kits fit a standard sink or counter hole. For thick stone, pick a long-shank body. Some bodies handle two dishwashers. With a one-hole sink, mount the cap on the counter behind the faucet or use a deck plate with an extra punch out.

Table Of Symptoms And Fixes

Symptom	Likely Cause	Quick Fix
Water at cap	Outlet path blocked	Clear the branch or disposer inlet; flush the hose
No drain, dry cap	Inlet path blocked	Straighten the hose; check the pump check valve
Leak under sink	Loose clamp or split hose	Re-clamp or replace the hose
Bad smell	Food trapped in outlet hose	Remove and rinse the hose and nipple
Loud gurgle	Partial clog at cap	Clean the insert and slots under the cap

When A High Loop Makes Sense

A high loop fastens the hose to the underside of the counter before the drop to the drain. The rise cuts backflow risk and saves a deck hole, but it relies on hose height and clamps that stay put. Busy sink bases can knock a loop loose.

Safe Use Habits

Do not cover the cap with a cup or a scrub sponge holder. Keep the vent open and dry. Run the disposer for a few seconds before each cycle to clear the grind chamber so chunks do not lodge in the branch. Once a month, run hot water down the sink while the machine drains. That brief flush helps move grease past the trap.

Quick Code Notes

The International Plumbing Code allows a dishwashing machine to drain through an air gap or air break to a receptor that meets the same chapter. The Uniform Plumbing Code calls for an air gap fitting in many homes. Cities post handouts that mirror those rules. Read your posted code pages and the maker’s sheet.

Final Checks After Install

Run two drain cycles while watching the cap and the cabinet. Check for leaks at each clamp. Confirm the outlet hose slopes down to the branch and that the branch sits above the trap arm. Wipe the cap dry and make sure no water returns after the pump stops.