Why Your Dishwasher Won’t Drain

Open the door at the end of a cycle, find a pool of cloudy water sitting over the bottom, and the instinct is to assume the machine is broken. Usually it is not. A dishwasher that will not drain almost always has a blockage somewhere along one short path: out of the tub, through a filter and sump, down a flexible hose, and into the same drain your kitchen sink uses. The water has nowhere to go, so it stays. Work that path in order, from the cheapest and safest checks to the ones that mean the repair is no longer yours, and you can usually find the cause without guessing.

One thing to settle first. A thin film of water in the sump well under the filter is normal and intentional. Manufacturers leave a small amount behind to keep the pump seals from drying out and cracking. What signals a drain problem is a real standing pool that covers the floor of the tub after a complete cycle, not a shallow ring at the lowest point. This guide assumes you are looking at the standing pool.

A quick scope note. This is the drain side. For how the supply and fill side works, see our guide on how dishwasher plumbing works (168). For what the countertop air gap is and the full reason it exists, see our guide on what a dishwasher air gap is and why it matters (170). Here, the air gap shows up only as one possible cause of the backup.

Start at the Bottom: Cleaning the Dishwasher Filter and Sump

The first thing to check, and the most common fix, is a clogged filter and sump at the bottom of the tub. Pull the lower rack and look at the floor of the dishwasher. Most machines made in the last decade have a removable cylindrical or flat filter assembly there, often a coarse outer filter you twist to unlock and a fine screen beneath it.

Lift the filter out and rinse it under the faucet. Food fragments, bits of paper from soaked container labels, grease, and hard mineral grit collect in the mesh and choke the water that is trying to leave. A soft brush or old toothbrush clears the screen without tearing it. With the filter out, look down into the sump, the small well underneath where water gathers before the pump moves it out. Wipe away any visible debris, broken glass, or a stray pit or seed with a paper towel or a wet/dry vacuum. Manufacturer guides from Whirlpool and Maytag treat this filter-and-sump clean as the first step for a dishwasher that will not drain, and it resolves a large share of cases on its own.

A practical habit prevents most repeat clogs. Scrape plates of large scraps before loading, and run the cycle with reasonably clear racks rather than relying on the machine to grind chunks. The filter is a strainer, not a disposer.

The New-Disposal Trap: The Knockout Plug Nobody Removed

If the dishwasher stopped draining right after a new garbage disposal was installed, suspect the knockout plug before anything else. This is the cause generic articles bury, and it explains a drain failure no amount of filter cleaning will fix.

A new garbage disposal ships with a solid molded plug sealing the small side inlet where the dishwasher drain hose connects. That plug exists so the disposal can be sold and used without a dishwasher attached. When a dishwasher is hooked to that inlet, the plug has to be knocked out, or the dishwasher drains straight into a sealed dead end and the water has nowhere to go. Maytag identifies a not-yet-removed disposal plug as a leading reason a newly installed dishwasher will not drain. Whoever swapped the disposal may simply have missed it.

You can confirm it without tools. With power off, slide a screwdriver into the disposal’s dishwasher inlet. If it stops against a wall instead of opening into the chamber, the plug is still there. Removing it is a manufacturer-described step on the disposal, not an appliance-internal repair: with the disposal switched off and its power cut at the outlet or breaker, the plug is tapped out from the inlet into the disposal chamber and then fished out so it cannot get caught in the grind components. If a new disposal is humming, jammed, or will not run at all rather than just blocking drainage, that is a different problem covered in our guides on a disposal that won’t turn on or is humming (046) and how to reset and unjam a garbage disposal (047).

Checking the Drain Hose for Kinks, Clogs, and a Missing High Loop

The next thing to inspect is the drain hose between the dishwasher and the sink drain or disposal, because a kink, a clog, or a missing high loop all stop water the same way. Ease the dishwasher out from under the counter far enough to see the corrugated hose, or open the sink cabinet to follow it.

Look for three things. First, a kink or a crushed spot where the hose is pinched behind the machine or pressed flat against a cabinet wall; even a small bend can hold water back. Straighten the routing and the drain may clear immediately. Second, a clog inside the hose or at its connection to the disposal or drain stub, often a wad of grease and food where the hose meets the fitting. Third, the high loop.

A high loop is the hose routed up high under the countertop and secured there before it drops down to the drain connection. That rise is what stops dirty water from the sink or disposal from siphoning backward into the dishwasher tub. The International Residential Code requires the dishwasher discharge to be protected against backflow, and it accepts either a high loop secured up under the counter or a separate air gap device above the counter (IRC Section P2717.2). Codes vary by jurisdiction, so confirm what your area adopts; some places, notably California, require an air gap and do not accept a high loop alone. If the hose is simply lying flat in the cabinet or sagging low, lift it and fasten it as high as it will go under the countertop. That single change resolves both backflow and slow draining in many homes.

If the dishwasher drains into the garbage disposal, run the disposal for a few seconds with cold water before suspecting the machine. The two share the same outlet, and a plug of food in the disposal throat can back water up into the dishwasher. Running it clears the shared path. For the sink drain itself being slow, that is a separate fix covered in our guide on how to unclog a kitchen sink (030).

When a Clogged Air Gap Is Backing Water Up

If your sink has a small chrome cylinder behind the faucet and water bubbles up around it during a cycle, a clogged air gap is backing the drainage up. The tell is specific: water spitting onto the counter from that little cap while the dishwasher runs, often alongside standing water left in the tub.

The air gap carries the dishwasher discharge up and over a physical break before it drops to the disposal or drain, and ground-up food and grease can build up inside it or in the larger hose just past it. When that passage narrows, the dishwasher cannot push water through, so it backs up and overflows the cap. Cleaning it is a homeowner task: pop the decorative cover off, unscrew or unsnap the cap underneath, and clear the visible gunk; a bottle brush works the inside, and the most common true blockage is in the wider hose running from the air gap to the disposal inlet, which can be detached and cleared. The full explanation of what the air gap is and why code may require it lives in our guide on what a dishwasher air gap is and why it matters (170).

When It’s the Pump or Drain Valve (an Appliance Repair, Not a Plumbing Fix)

If the filter and sump are clean, the disposal plug is out, the hose is clear and looped high, and the air gap is open, but the water still will not leave, the problem is most likely the drain pump or the drain valve inside the machine. This is where the job stops being a plumbing check and becomes an appliance repair.

The drain pump uses a motor-driven impeller to push water out of the tub and through the hose. The drain valve, on machines that use one, opens to let the water out, often through a solenoid. When the impeller is cracked or jammed by a sliver of glass or a fruit pit that slipped past the filter, or when the pump motor or the valve solenoid fails electrically, the water has a clear path but nothing to move it. These are sealed, motor-and-electrical components reached by partially dismantling the dishwasher, and they are diagnosed and replaced as appliance parts, not as household plumbing. The right person here is the appliance manufacturer’s service line or a qualified appliance repair technician, who can confirm whether the pump, the impeller, or the valve is at fault and fit the correct part.

Do not start pulling the machine apart to reach the pump, and do not run repeated cycles hoping it clears, which can overheat a straining motor. You have done the part that is genuinely yours when you have cleared the filter, sump, hose, high loop, air gap, and disposal path. What remains is inside the appliance.

Frequently Asked Questions

Why is there standing water in the bottom of my dishwasher?

A small film of water in the sump well under the filter is normal and left there on purpose to protect the pump seals. A real standing pool covering the floor of the tub after a full cycle means the water cannot drain. The usual causes, in the order worth checking, are a clogged filter and sump, a garbage disposal knockout plug that was never removed, a kinked or clogged drain hose or a hose that is not looped up high, a clogged air gap, and finally a failed drain pump or valve inside the machine.

Do I have to remove a plug when connecting a dishwasher to a new disposal?

Yes. A new garbage disposal comes with a solid knockout plug sealing the dishwasher drain inlet so it can be used without a dishwasher. When you connect a dishwasher to that inlet, the plug has to be knocked out first, or the dishwasher drains into a sealed dead end and the water backs up. With the disposal’s power cut, the plug is tapped out of the inlet into the chamber and then removed so it does not jam the unit.

Is it safe to clean the dishwasher filter and sump myself?

Yes. Removing the filter, rinsing it, and wiping debris from the sump well is a manufacturer-described maintenance task that needs no tools beyond a brush and no work on any pressurized or electrical part. The boundary is the pump and drain valve inside the machine, which are appliance-internal repairs for a technician, not a homeowner cleaning job.

This article is general information, not professional advice. When a repair involves the internal pump, motor, or electrical parts of an appliance, or work governed by local plumbing code, consult the appliance manufacturer’s service line or a licensed professional.

Sources

Maytag, Newly Installed Dishwasher Not Draining (garbage disposal knockout plug and new-install drain failures): https://producthelp.maytag.com/Dishwashers/ProductInfo/DishwasherProductAssistance/NewlyInstalledDishwasherNotDraining
Whirlpool, How to Unclog a Dishwasher Drain in 5 Steps (filter and sump cleaning, drain hose, disposal connection): https://www.whirlpool.com/blog/kitchen/how-to-fix-a-clogged-dishwasher.html
Maytag, How to Unclog a Dishwasher That Won’t Drain (filter, drain hose, and disposal checks): https://www.maytag.com/blog/kitchen/how-to-fix-a-clogged-dishwasher.html
Whirlpool, Checking the Drain Loop Height (high loop guidance for the dishwasher drain hose): https://producthelp.whirlpool.com/Dishwashers/ProductInfo/DishwasherProductAssistance/CheckingtheDrainLoopHeight
ICC, International Residential Code, Section P2717.2 Sink and Dishwasher (backflow protection by air gap or high loop; jurisdiction-adopted): https://codes.iccsafe.org/s/IRC2021P2/chapter-27-plumbing-fixtures/IRC2021P2-Pt07-Ch27-SecP2717