How to Connect a Dishwasher Drain Hose to a Garbage Disposal
It is a 30-minute job for most people, but two details decide whether it works: the knockout plug and the high loop.
To connect a dishwasher drain hose to a garbage disposal, remove the disposal’s knockout plug, route the hose up in a high loop or through an air gap, slide it onto the disposal’s dishwasher inlet and tighten a hose clamp over it. For most people it takes 20 to 45 minutes. Switch off power to both the disposal and the dishwasher before you start, and run a full test for leaks before you put the cabinet back together.
The step people skip is the knockout plug. A new disposal ships with that inlet sealed, and if you connect the hose without removing the plug, the dishwasher has nowhere to drain and will hold water or overflow.
How the connection works
Most disposals have a short, angled nipple on the side near the top of the grinding chamber. That is the dishwasher inlet. When the dishwasher pumps out, its dirty water enters the disposal and flows out through the disposal’s discharge pipe into the sink trap. The hose has to be routed so that water from the sink and disposal cannot flow back down into the dishwasher. That is the job of the high loop or air gap.
What you need
- Flathead screwdriver and a hammer (for the knockout plug)
- Pliers or needle-nose pliers to fish out the plug
- A stainless steel screw-type hose clamp sized to fit over your hose on the inlet
- Nut driver or screwdriver for the clamp
- Flashlight, towel and a shallow pan
- Rubber adapter, if your hose end does not fit the inlet snugly
- Your disposal and dishwasher manuals (the model number is on a label on the disposal body and inside the dishwasher door frame)
Step-by-step
- Cut the power. Unplug the disposal under the sink or switch off its breaker. Do the same for the dishwasher. If you are not sure which breaker is which, see our guide to working with your breaker panel.
- Remove the knockout plug if it is still there. Shine a light into the dishwasher inlet. If you see a solid plastic wall, the plug is in place. Tap it out with a screwdriver and hammer, then retrieve the loose piece from inside the disposal. Our knockout plug guide walks through it in detail.
- Set up the high loop or air gap. For a high loop, fasten the drain hose to the underside of the countertop or the highest point of the cabinet with a strap or clamp, so the hose rises well above the disposal inlet before dropping down to it. For an air gap, run a hose from the dishwasher to the air gap’s smaller inlet, and a second hose from the larger outlet down to the disposal.
- Slide the hose onto the inlet. Push it fully over the nipple. If the fit is loose, use the rubber adapter that came with the dishwasher or one sold for this purpose.
- Clamp it. Place the hose clamp just behind the raised lip of the inlet and tighten until snug. Overtightening can cut the hose or crack a plastic inlet.
- Check the hose path. No kinks, no sags that dip below the disposal inlet, and no sharp bends where it passes through the cabinet wall.
- Restore power and test. Run water in the sink, run the disposal briefly, then start a short dishwasher cycle and let it pump out. Watch the inlet connection with a dry paper towel.
High loop or air gap?
Both aim to stop backflow, but they work differently, and local code decides which you need.
| Option | How it works | Pros | Cons |
|---|---|---|---|
| High loop | Hose rises to the underside of the counter, then drops to the disposal | No extra parts, nothing on the sink deck | Relies on elevation; no physical break in the line |
| Air gap | A fitting on the sink deck creates an open break between dishwasher and drain | True physical separation; a clog shows up as water spilling at the sink rather than in the dishwasher | Needs a hole in the sink or counter; can drip or gurgle if its outlet clogs |
Plumbing codes differ. Jurisdictions that follow the Uniform Plumbing Code generally require an air gap, while the International Plumbing Code allows a high loop in many places. Your local building department can tell you what applies, and the dishwasher’s installation instructions usually state a minimum loop height.
Mistakes that cause trouble
- Leaving the knockout plug in. The dishwasher will not drain. This is the most common reason a new disposal “breaks” a dishwasher.
- No loop at all. The hose runs low and flat, and disposal water can siphon back into the dishwasher, causing smells and dirty water in the tub.
- Kinked or crushed hose. Slows drainage and leaves standing water. If that has already happened, see how to drain a dishwasher with standing water.
- Reusing a weak clamp. Old spring clamps lose tension. A new screw clamp costs little.
- Extending the hose with mismatched parts. Use only the extension method the dishwasher maker approves.
Testing for leaks
InSinkErator’s own support advice for leaks at this inlet is a good checklist: confirm the knockout plug is gone, check that clamps are tight, check any hose adapter for damage, and check the joint between the disposal outlet and the trap. A simple trick is to lay newspaper or paper towels flat on the cabinet floor and leave them for a day or two; drips leave obvious marks. InSinkErator describes this approach on its dishwasher inlet leak page.
If water appears somewhere else, such as from the bottom of the disposal, use our guide to a garbage disposal leaking from the bottom to pin it down.
When to call a pro
- Your local code requires an air gap and your sink has no spare hole, so drilling stone or a sink is involved.
- The dishwasher drain line is too short and needs rerouting through cabinets.
- You find corroded drain pipes, a cracked disposal inlet or signs of water damage in the cabinet floor.
- The electrical connection to the disposal or dishwasher looks damaged or improvised. That is a job for a licensed electrician.
A plumber can usually do this connection quickly as part of a disposal or dishwasher install. Rates vary widely by region, so ask for a quote up front.
Bottom line
Power off, knockout plug out, high loop or air gap in place, hose clamped on the inlet, then test with a real dishwasher drain cycle. If the dishwasher leaves water behind after the hookup, the knockout plug or a kink in the hose is almost always the culprit.
FAQ
Do I need to remove the knockout plug on a used disposal?
Only if it is still there. If the disposal was previously connected to a dishwasher, the plug is probably already gone. Check with a flashlight before you hammer anything.
Can I connect the dishwasher hose to the sink drain instead?
Yes, many installs use a sink tailpiece with a dishwasher branch when there is no disposal. With a disposal present, the disposal inlet is the usual connection point. Follow your dishwasher’s installation instructions and local code.
Why does my dishwasher smell after connecting it?
Usually because the hose has no high loop and sink water is draining back into the dishwasher. Raise the loop and run an empty cycle.
What size clamp do I need?
It depends on the hose and the inlet, and sizes vary between brands. Measure the outside of the hose once it is pushed over the inlet, or take the hose end to the store, and buy a screw clamp whose range covers that measurement.
