What are expert tips for dishwasher drain connection?

Always check inside the disposal for the knocked-out plug disc. If it stays in there, it'll jam the disposal the first time you run it. A high loop is the easiest backflow prevention and works in most jurisdictions. If the dishwasher drain hose is kinked or too long, replace it with a new one -- they're under $10.

What mistakes should I avoid with dishwasher drain connection?

Forgetting to knock out the disposal drain plug -- causes dishwasher backup on the very first cycle. Not creating a high loop or air gap -- allows dirty sink water to siphon back into the dishwasher. Loose hose clamp connection that drips behind the dishwasher unnoticed. Leaving the knocked-out plug disc inside the disposal.

Dishwasher Drain Connection | The Plumbing Directory

Overview

Connecting a dishwasher drain line to a garbage disposal is a quick job, but doing it wrong causes one of the most common kitchen plumbing complaints we see: dirty water backing up into the dishwasher. The fix is simple -- you just need the right connection method and a high loop or air gap to prevent backflow.

What to Know

With a Garbage Disposal

If you have a disposal, the dishwasher drain hose connects to a small inlet on the side of the disposal. Before connecting, you have to knock out the drain plug inside that inlet -- it's a perforated disc. Use a screwdriver and tap it with a hammer, then reach in and remove the disc. Skip this step and the dishwasher water has nowhere to go.

Without a Garbage Disposal

No disposal? The dishwasher drain connects to a tailpiece with a dishwasher inlet branch -- it's a Y-shaped fitting that goes between the sink strainer and the P-trap. This is a standard part you can find at any hardware store.

High Loop vs Air Gap

To prevent dirty sink water from flowing back into the dishwasher, the drain hose needs either a high loop (loop the hose up as high as possible under the counter and secure it) or an air gap device (a small cylinder mounted on the countertop or sink). Some local codes require an air gap; others accept a high loop. Check your code.

Tools & Materials

Hose clamp
Screwdriver
Dishwasher drain hose (if not included)
Air gap fitting (if required by code)

Step by Step

Knock out the disposal drain plug (if applicable)
With the disposal disconnected from power, insert a screwdriver into the dishwasher inlet inside the disposal. Tap firmly with a hammer to pop out the plug disc. Fish it out so it doesn't jam the disposal.
Route the drain hose
Run the dishwasher drain hose from the dishwasher to the disposal or tailpiece inlet. Create a high loop by securing the hose as high as possible under the countertop with a hose clamp or bracket.
Connect the hose
Slide the drain hose onto the disposal inlet or tailpiece branch. Secure with a hose clamp. Make sure the connection is tight -- a loose hose causes leaks that drip behind the dishwasher where you won't notice them for weeks.
Test
Run the dishwasher through a short cycle. Check the connection at the disposal for leaks. Run the disposal while the dishwasher is draining to make sure water flows through properly.

Pro Tips

Always check inside the disposal for the knocked-out plug disc. If it stays in there, it'll jam the disposal the first time you run it.
A high loop is the easiest backflow prevention and works in most jurisdictions.
If the dishwasher drain hose is kinked or too long, replace it with a new one -- they're under $10.

Mistakes to Avoid

Forgetting to knock out the disposal drain plug -- causes dishwasher backup on the very first cycle.
Not creating a high loop or air gap -- allows dirty sink water to siphon back into the dishwasher.
Loose hose clamp connection that drips behind the dishwasher unnoticed.
Leaving the knocked-out plug disc inside the disposal.

When to Call a Pro

This is one of the simpler plumbing connections out there. The only time you'd need a pro is if your drain configuration is unusual or if you need to install an air gap and aren't comfortable drilling through a countertop or sink.

Bottom Line

A dishwasher drain connection is a 15-30 minute job. Knock out the disposal plug, create a high loop, secure the hose clamp. That's it. Most dishwasher backup issues trace back to one of these three steps being missed.

Dishwasher Drain Connection