Different Methods for Dishwasher Drain Connections (2024)

FAQs

Different Methods for Dishwasher Drain Connections? ›

The different drain variations you may encounter include: Drain line connected through an air gap to the garbage disposal. Drain line connected through an air gap directly to the drain. Drain line configured in a "high loop" to the garbage disposal.

Dishwashers need a high loop under the sink to help prevent back-siphoning of drain water back to the dishwasher. So your hose should be oriented such that it goes into your sinkbase cabinet through a hole high up--just under the counter--then down into either the tailpipe of a basin drain line or the waste disposer.

However, high loops are popular, inexpensive to install and have proven to be reliable backflow prevention methods. If you opt not to install a dishwasher air gap, a high loop is the best alternative.

So again, while there is nothing in the code that says you can't run the drain directly into the waste line, it is almost always easier and certainly less complicated to connect the dishwasher drain hose to the drain at the kitchen sink.

An air-gap is essentially the same as a high loop however it extends above the counter top and has a gap in the piping.

The hose should be run as high as possible in your cabinet, forming an arcing loop, which you can affix with clamps.

On the loose end of the dishwasher drain hose, find the correct size ring that fits the air gap fitting and cut away the portion you don't need with your utility knife. Slip a hose clamp over the end of the hose and slide the hose onto the small-diameter side of the air gap fitting. Tighten the clamp.

The high loop is necessary for 2 reasons. The first is to ensure proper drainage of waste water during the drain cycle and prevent siphoning. The second is to prevent contaminated water from the garbage disposal or sink drain from back-flowing into the dishwasher.

In California, Washington, Minnesota and Hawaii, a dishwasher air gap is a mandatory residential plumbing procedure. Here in California, I've had numerous customers ask me to install air gaps for them, because big box store contractors refuse to hook up a dishwasher without one.

Dishwasher Drain Connection Types

The four common configurations include high loop to disposal, high loop to drain, air gap to disposal, and air gap to drain.

Can a dishwasher drain into a standpipe? ›

Dishwashers may drain into a standpipe complying with Section P2706. 2 as shown in the following illustration. The standpipe shall be provided with an air break (with drain hose secured to the underside of the counter top) or air gap as shown in the illustration below.

A dishwasher does not have a separate drain as part of your home's plumbing system. Instead, it drains through the disposal. That includes any food debris washed off the plates and bowls during the cleaning cycle. When the disposal is draining slowly or is clogged, those problems can affect the dishwasher.

The dishwasher drain hose connects to the sink drain before the P-trap. If the sink has a garbage disposal, you should find an inlet port on it for the dishwasher drain hose, but if there's no garbage disposal, you have to connect the drain hose to the drain tailpiece, which involves installing a tee.

If the drain hose is too low under the sink or doesn't have the correct loop height, gravity can cause water to flow back into the sink. Solution: Adjust the drain hose loop according to the dishwasher manufacturer's instructions. This will create a higher point in the hose, preventing water from flowing backward.

The high loop is necessary for 2 reasons. The first is to ensure proper drainage of waste water during the drain cycle and prevent siphoning. The second is to prevent contaminated water from the garbage disposal or sink drain from back-flowing into the dishwasher.

**Proper Drainage:** Dishwashers discharge water with detergent and food residue, which can accumulate over time. A separate P-trap allows for efficient drainage, ensuring that wastewater flows smoothly into your sewage system, preventing backups and odors.

The dishwasher drain must be connected before the P-trap, not after it, which is what was done here. With this improper installation, sewer gases have the potential to come back in to the dishwasher. The diagram below right shows a proper installation.