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, while the air gap is a separate fitting that breaks the line open to the air. Installation guides specify one or the other, with minimum heights, because a drain hose run low and straight to the sink drain can siphon.
What the spec actually says
- •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.
Why manufacturers require it
- •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 it 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.
How to check your home against it
- Open the sink cabinet and trace the dishwasher drain hose from the side wall to where it connects.
- 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.
- Look at the sink deck for a small cylindrical cap near the faucet. That's an air gap, and the hose should run to it.
- 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.
When it needs a licensed pro
- •Plumbing codes vary by town, and some require an air gap regardless of what the dishwasher guide allows. A licensed plumber or your local building department can tell you which applies.
- •Installing an air gap means drilling the countertop or sink and connecting it to the drain. That's plumbing work.
- •A waste tee that sits too low, or a sink drain that needs re-piping, is a job for a plumber.
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, it needs a loop or an air gap.
Standing water in the tub, or sink water backing into it, after the hose is routed correctly calls for a closer look at the pump and drain path. Book through our dishwasher repair page or call TrueFix Long Island at (631) 985-3690.