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

An inch or so in the sump after a cycle can be normal by design; a basin full is a drain problem, worked from the filter to the hose to the disposal connection, with the pump last on the list.

Why did my dishwasher stop draining after a new garbage disposal?

The disposal's dishwasher inlet ships plugged with a knockout, and installers forget it constantly. If the timing matches a disposal swap, the knockout is the diagnosis until proven otherwise.

How do I clean a dishwasher filter?

Twist out the cylindrical filter assembly in the tub's floor, rinse under the faucet, brush the fine screen, and reseat. Monthly in food-heavy households; the filter is the number one drain suspect.

What is the loop or air gap in the dishwasher drain hose for?

Backflow prevention: the high loop under the counter, or the air gap fitting at the sink, keeps sink drain water from siphoning into the dishwasher. A missing high loop causes both drain-back and dirty-water mysteries.

Dishwasher Not Draining: The Checklist

Page last reviewed: August 2026 · Reviewed by Harold R. Bennett, retired home inspector

A dishwasher that will not drain is a short-path problem: the water leaves through one filter, one pump, one hose, and one connection at the sink, and the whole route is checkable in half an hour with a towel and a flashlight. Dishwasher not draining calls resolve overwhelmingly at the cheap end of that path, with one famous installer’s mistake owning a share all its own. This diagnostic works the route in order.

First, what counts as a problem

A small amount of water in the sump, the low well under the filter, is normal on many designs, kept there to protect seals. The complaint that counts is a basin holding standing water after a completed cycle, dishes sitting in gray soup, or a cycle ending early with drain errors on the display, and the first move is mechanical triage: bail or wet-vac the standing water so the path can be inspected dry, and run the drain-only or cancel cycle while listening, a humming pump that moves nothing versus silence being the first fork in the diagnosis.

The checklist, cheap end first

One: the filter. The cylindrical filter assembly in the tub floor twists out; food debris, labels, seeds, and glass shards mat its screens and are the leading cause in every service ranking. Rinse, brush, check the sump beneath for debris (spoon fragments and broken glass collect there and can jam the impeller below), and reseat. Monthly cleaning is the ownership habit that retires most of this article.

Two: the sink connection, and the knockout. The drain hose ends at the sink’s plumbing, either at a branch tailpiece or, most commonly, at the garbage disposal’s dishwasher inlet, and that inlet ships from the factory plugged with a knockout that must be punched out at installation. A dishwasher that stopped draining right after a disposal replacement has its diagnosis in the timing: hose clamp off, knockout punched with a screwdriver and mallet, the plug fished out of the disposal, done. A clogged disposal or slow sink drain blocks the same doorway without the knockout’s excuse, so the sink side gets run and verified regardless.

Three: the hose. Kinks behind and under the machine (common after the unit has been slid in hard), and clogs at the hose’s low points and at its connection ends, clear by disconnecting at the sink end over a bucket and blowing or snaking through. While there, verify the high loop: the hose should rise to the underside of the countertop before dropping to the connection (or pass through an air gap fitting where local practice requires the chrome cylinder at the sink), the backflow detail that prevents sink water siphoning back into the machine, whose absence explains the adjacent mystery of a dishwasher that fills itself with dirty water between cycles. Air gaps clog too, cap off, debris out.

Four: the pump. With filter, connection, and hose exonerated, the drain pump takes the stand: glass or a fruit pit jamming the impeller (often reachable from the sump with the power off), a failed pump motor (the hum-but-no-flow or dead-silence findings), or a check valve stuck shut. Impeller obstructions are homeowner-plausible with the manual’s guidance and the breaker off; pump replacement is a parts-and-patience job or a service call, priced against the repair-or-replace math on machines past mid-life.

The habits that prevent the rerun

Scrape (not pre-rinse, but scrape) plates, clean the filter monthly, run hot water at the sink before starting so the machine fills hot, run the disposal before the dishwasher when they share a drain, and glance under the sink yearly at the hose’s loop, clamps, and the connection’s tightness, the same visit that checks the supply line and valve feeding the machine, and the natural moment to consider a leak detector on the cabinet floor, dishwasher bays being classic slow-leak country.

The bottom line

Filter, knockout, hose, pump, in that order: rinse the screens monthly, punch the knockout after every disposal swap, keep the high loop high, and save the pump’s autopsy for last. The path is three feet long and mostly cleans with a brush, which is the right scale of repair for the most common kitchen-appliance complaint there is.