A dishwasher high loop and an air gap are two ways of keeping dirty sink and disposer water from flowing back into the dishwasher. The loop raises the drain hose up under the countertop. The air gap is a separate fitting, usually a small chrome cap on the sink deck, that breaks the line open to the air. Installation guides specify one or the other because a drain hose run low and straight to the sink drain can siphon.
If you've lived in California for a while, you've probably noticed that little cap next to the faucet in most kitchens. That's not a coincidence, and it's worth understanding before you replace a dishwasher or remodel a sink.
What the manufacturer specs say
- •GE GLD6500: GE's instructions route the hose through the required 32-inch minimum height and say an air gap must be used if the waste tee or disposer connection is less than 18 inches above the floor to prevent siphoning. They add that the disposer drain plug must be removed, or the dishwasher won't drain, and that the total distance to the drain shouldn't exceed 10 feet.
- •Whirlpool-published undercounter dishwasher guide (W10702387): It says to connect the drain hose above the drain trap, loop it up and fasten it under the counter, or connect it to an air gap. It also calls for an air gap if the house connection is lower than 18 inches above the floor. The guide gives 32 inches as the minimum in one place and "at least 20 inches above the floor" in the steps, so use the figure for your model's diagram.
- •Bosch SHE53T56UC: Bosch's spec sheet says to raise a portion of the drain hose between a minimum of 20 inches and a maximum of 43 inches above the cabinet floor, and notes that plumbing installations vary, so refer to local codes.
Note the reference point. GE and Whirlpool measure from the floor, while Bosch measures from the cabinet floor.
How each one works
- •Siphoning: A hose that runs down to a drain connection can act like a siphon, pulling water out of the dishwasher in the middle of a cycle.
- •Backflow: When the sink is full or the disposer runs, water can push back up a low hose into the dishwasher. A high loop makes that water climb first. An air gap opens the line to the air, so water physically can't be pulled back.
- •Pump limits: The maximum heights and lengths keep the drain pump working within what it can lift and push.
- •The knockout plug: New disposers ship with a plug in the dishwasher inlet. Leave it in, and the dishwasher can't drain at all.
A high loop reduces the risk. An air gap removes the direct connection entirely, which is why plumbing codes tend to favor it.
Air gaps in California and San Diego
California's plumbing code has long favored a separate air gap fitting on residential dishwasher drains, where many manufacturer guides accept a high loop, and that is a large part of why air gaps are so common in San Diego kitchens. Local rules and code editions vary, though, so don't assume either answer. Whether a high loop alone is acceptable for your installation depends on the code your city enforces and on when and how the work was permitted. Before you remove an air gap or install a dishwasher without one, check with the City of San Diego or your city's building department, or ask a licensed plumber who works locally.
Air gaps and hard water
Air gaps have a known downside: they can clog. Food debris and San Diego's mineral-heavy water build up in the small passage between the air gap and the disposer, and when the dishwasher pumps out, water spurts from the cap onto the counter. That's almost always a blockage downstream of the air gap, often in the hose to the disposer or at the disposer inlet, not a dishwasher failure.
How to check your setup
- Open the sink cabinet and trace the dishwasher drain hose from the side wall to where it connects.
- Look at the sink deck for a small cylindrical cap near the faucet. That's an air gap, and the hose should run up to it.
- If there's no air gap, find the highest point of the hose and measure from the floor (or the cabinet floor, for Bosch) to the top of that loop.
- Check that the loop is fastened up under the counter or to the cabinet, not resting on the cabinet floor.
- Measure the height of the waste tee or disposer inlet where the hose connects. Below 18 inches, GE and Whirlpool call for an air gap.
- On a new disposer, confirm the knockout plug was removed.
What happens when it's ignored
- •Dirty water from the sink or disposer ends up in the dishwasher tub.
- •Water sits in the bottom after the cycle, and odors build.
- •The dishwasher can drain while it's trying to fill, leading to poor cleaning or fill errors.
- •A new install with the knockout plug still in place won't drain at all.
The loop and hose have to fit inside the cabinet opening too. See dishwasher cutout dimensions.
Troubleshooting common drain complaints
| Symptom | Likely cause to check first |
|---|---|
| Water spurts from the air gap cap | Clog between the air gap and the disposer or drain |
| Standing water after every cycle | Drain hose kinked, filter clogged, or knockout plug left in |
| Sink water backs into the dishwasher | No high loop or air gap, or the hose has slipped down |
| Dishwasher drains during fill | Siphoning from a low hose |
| Drains slowly, gurgles | Partial clog in the sink drain or disposer |
What we check on a service visit
When a dishwasher won't drain or smells, we check the whole path, not just the machine:
- •The filter and sump for debris.
- •The drain pump and its check valve.
- •The hose route, loop height and any kinks behind the unit.
- •The air gap and the connection to the disposer or waste tee.
If the blockage is in the house drain beyond the dishwasher, we'll tell you it's a plumber's job. Our dishwasher repair page has more on drain faults, and owners of GE models can see GE dishwasher repair.
When a plumber is needed
- •Installing an air gap means drilling the countertop or sink and connecting it to the drain. That's a job for a licensed plumber.
- •A waste tee that sits too low, or a sink drain that needs re-piping, is a job for a plumber.
- •A clog beyond the disposer, in the sink drain or the line in the wall, needs a plumber.
Frequently asked questions
Can I remove the air gap and just use a high loop?
Not without checking local requirements first. The dishwasher guide may allow a high loop, but the code your city enforces may not.
Why does my air gap leak only when the dishwasher drains?
Because that's the only time water flows through it. A leak at that moment almost always means the outlet side is partly blocked. Clearing the hose to the disposer, or the disposer inlet itself, usually solves it.
Sources
- •GE: GLD6500 installation instructions (32-inch loop; air gap below 18 inches; knockout plug; 10-foot limit)
- •Whirlpool: Undercounter dishwasher installation instructions W10702387 (loop or air gap; connection above the trap; 18-inch rule)
- •Bosch: SHE53T56UC spec sheet (20 to 43 inches above the cabinet floor; local codes)
Quick check: Look under the sink. If the drain hose lies on the cabinet floor all the way to the drain and there's no air gap on the sink, it needs a loop or an air gap.
Standing water in the tub after the hose is routed correctly calls for a closer look at the pump and drain path. You can book a visit online and we'll track it down.