How to Fix a Dishwasher That Won't Drain: 5-Step Diagnosis (2026)

Frequently Asked Questions

Where is the dishwasher filter and how do I clean it?

Most modern dishwashers have a cylindrical filter assembly at the bottom of the tub (under the spray arm). It consists of a round coarse filter (removes large debris) and a fine mesh filter below. To clean: turn the coarse filter counterclockwise and lift out. Remove the fine filter beneath it. Rinse both under running water — use a soft brush (old toothbrush) on the mesh filter. Reinstall: place fine filter back, set coarse filter in, turn clockwise to lock. This should be done monthly to prevent buildup.

What is the garbage disposal knockout plug issue?

When a new garbage disposal is installed, the dishwasher drain port on the disposal side has a plastic knockout plug installed from the factory — it must be knocked out before connecting the dishwasher drain hose. If you recently replaced your disposal and the dishwasher stopped draining: the knockout plug was never removed. Fix: disconnect the drain hose from the disposal, look into the disposal inlet, and knock out the plastic plug with a screwdriver and hammer. Reconnect the hose.

How do I check the drain hose for kinks or clogs?

The drain hose runs from the dishwasher pump to either the garbage disposal or a branch at the sink drain. Access it by removing the kickplate at the base of the dishwasher (two screws). Look for: kinks where the hose makes the turn to the cabinet wall, and ensure the hose is looped up to the top of the cabinet before dropping down to the connection point (the high loop prevents backflow). Disconnect the hose and blow through it — if there is resistance, the hose is clogged. Clear with a plumber's snake or replace the hose ($10–$20).

What is the dishwasher air gap?

An air gap is a chrome cylinder mounted through the countertop or sink near the faucet. It prevents contaminated sink water from siphoning back into the dishwasher. The top cover pops off (or unscrews) revealing two hose connections inside. If the air gap is clogged with debris, water backs up into the dishwasher instead of draining. To clean: remove the cap and cover, clear debris from inside the air gap body with a brush or toothpick. Not all installations have an air gap — check if yours does.

My dishwasher drains but slowly. What causes that?

Slow drainage is usually a partial clog — clean the filter thoroughly (see above). Also check: (1) The sink drain itself — if the kitchen sink drains slowly, the shared drain is partially clogged and the dishwasher backs up into the slow drain. Clear the sink drain first. (2) The air gap — clean it as described above. (3) The drain hose connection at the disposal — food debris can accumulate where the hose enters the disposal. Disconnect and clear.

Standing water in the dishwasher is almost always a clog. Work through this sequence.

Step 1: Clean the filter (start here)

1. Open the dishwasher and remove the bottom rack.
2. Locate the filter assembly at the bottom of the tub — usually in the center-back or center.
3. Twist the coarse filter counterclockwise and lift out.
4. Lift out the flat fine-mesh filter beneath it.
5. Rinse both filters under hot running water. Scrub gently with a soft brush.
6. If grease-coated: soak in warm water with dish soap for 5 minutes, then scrub.
7. Reinstall filters. Lock the coarse filter clockwise.

Run a rinse cycle and check if water drains.

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Step 2: Check the garbage disposal connection

If the dishwasher drain hose connects to the garbage disposal:

1. Run the garbage disposal for 30 seconds — food buildup in the disposal can back water into the dishwasher drain.
2. If disposal was recently replaced: check for the knockout plug (see FAQ).

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Step 3: Check the air gap (if present)

Look for a chrome cylinder on the countertop near the faucet.

1. Unscrew or pop off the decorative cap.
2. Unscrew the plastic cover.
3. Look inside — clear any debris with a brush or toothpick.
4. Reassemble.

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Step 4: Inspect the drain hose

Remove the kickplate (bottom front panel — two screws). Trace the drain hose:

• Confirm it loops up to the top of the cabinet before dropping to the connection point (the high loop).
• Look for any kinks or sharp bends.
• Disconnect the hose at the disposal or sink drain end and check for debris at the connection point.

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Step 5: Check the kitchen sink drain

If the kitchen sink drains slowly, that backs up the dishwasher too. Clear the sink drain:

• Try a sink plunger first.
• Pour boiling water down the drain.
• Use a drain snake for stubborn clogs.

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Related guides

• How to Install a Dishwasher — full installation guide if replacing
• How to Replace a Garbage Disposal — if the disposal is the root cause
• How to Unclog a Kitchen Sink — clear the shared drain