Dishwasher Not Draining? One to Two Cups of Water Is Normal

Before anything else: some standing water is supposed to be there. GE states it directly — “Some water (standing water), usually one to two cups, remaining in the bottom of the Dishwasher tub is normal.”

It sits in the sump and keeps the seals in that area from drying out. If you have roughly a cupful of clean water at the bottom and the dishes came out clean, your dishwasher is working.

The fault GE describes is different and specific: dirty water building up over time, on an installation without a working air gap or a high enough drain loop. That is not a machine that failed to drain. That is a machine that drained and then got the water back.

Which points at the two checks below, and they are both free.

If the dishwasher is new: the knockout plug

This is the single most common cause of a dishwasher that has never drained properly, and the manufacturer says so plainly.

A garbage disposal ships from the factory with its dishwasher inlet sealed by a plug. It is there so that a disposal installed without a dishwasher does not leak from an open port. When a dishwasher is connected, that plug has to be knocked out first.

Whirlpool’s wording:

Removing the knock-out plug is critical for draining the dishwasher. This sometimes-neglected step is a common misdiagnosis for a clogged or not-draining dishwasher.

When it is missed, the drain hose is clamped tightly onto a sealed port. The pump runs, the machine sounds completely normal, and nothing moves. People go looking for a failed pump.

The tell is timing. If the dishwasher has never once drained properly since it was installed — or since a new disposal went in — check this before anything else. If it drained fine for two years and stopped last week, the plug is not your problem.

The 20-inch rule

Here is the specification that explains most of the rest, and almost nobody measures it.

Whirlpool’s requirement: the drain loop should be at least 20 inches from the floor to the highest point of the drain hose. And if it cannot be:

If under 20“, make sure to use an air gap.

The reason is siphoning. The drain hose has to rise higher than the water level in the tub before it falls to the drain, so that gravity cannot pull wastewater back down into the machine. Whirlpool describes it as preventing water being drawn back in by pressure changes.

Get under the sink and look at how the hose is routed. What you want to see is the hose climbing to a high point — clipped to the underside of the counter or to the cabinet wall — before dropping to the disposal or drain. What you often find instead is a hose running more or less straight across, because there was nothing holding it up and it sagged.

A sagging hose does not stop the pump working. It lets the water come back after the pump stops, which is why this fault presents as “it drains and then there is water again in the morning” rather than as an obvious failure.

The air gap, if you have one

The small chrome cylinder on the sink deck next to the tap. It does the same job as the high loop by a different route, and many local codes require one.

They collect debris, and a blocked one produces exactly this symptom. Twist the cover off, lift the cap underneath, and clear out anything in there. It takes two minutes and it is the most-ignored serviceable part in the kitchen.

The disposal itself

If the dishwasher drains into a garbage disposal, they share an outlet — and a clogged disposal stops the dishwasher draining. Whirlpool’s step is to run the disposer to clear the drain system.

Do that before running the dishwasher rather than after. Anything sitting in the disposal is in the dishwasher’s drain path.

The hose, along its whole run

Whirlpool’s instruction is to confirm the hose is not “pinched, crushed, or sharply bent” and that it is “securely clamped” to the sink drain or disposal inlet.

Two places to look, and people usually check only one:

• Under the sink, where it is easy to see and where a stored bucket or bottle of cleaner leans against it.
• Behind the dishwasher, where it is not. A machine pushed back into its housing after being pulled out crushes its own hose against the wall, which is why this fault so often follows some other job.

Then the sump and filter

Now the physical clearing, and this is where the power goes off.

1. Switch off at the breaker. You are putting your hands in water inside a live appliance.
2. Bail the standing water out with a cup and towels.
3. Take out the lower rack and look at the sump area at the back of the tub. Whirlpool’s guidance is to make sure nothing is covering or blocking it — a fallen label, a piece of plastic packaging, a lid.
4. Clear out food debris. Noodles, lettuce leaves, bones and fruit stickers are the recurring cast.
5. Remove and clean the filter.

Watch for glass. Chipped and broken glass migrates to the sump and it is invisible in dirty water. Use a cup and a cloth, not your fingers, and never push your hand into a space you cannot see into.

When the machine tells you itself

Many dishwashers report a drain failure as a code rather than leaving you to work it out — and the code is worth reading first, because it can distinguish a drain fault from a fill fault that looks similar.

If yours has a display or a blinking light pattern, see how to find your dishwasher’s error code before you start bailing.

On an LG the code for this is OE, and LG’s geometry rules are not the ones quoted above — it specifies the hose end between 12 and 40 inches measured from the base of the appliance, rather than a 20-inch loop measured from the floor. See the LG OE error code, which also covers a figure LG prints incorrectly on its own page.

Which of these is yours

Roughly a cup of clean water, dishes clean. No fault. This is the answer for a meaningful share of people searching this.

Water under the machine rather than in it. Different fault entirely, and a more serious one. On a Bosch that reports itself as an E15 code — a leak detected in the base, where the correct response is to shut the water off rather than to clear the code.

Never drained since it was installed. The knockout plug, and Whirlpool already told you it is the common misdiagnosis.

Drains, then refills itself overnight. The drain loop height or a blocked air gap. Free to fix, and it is the cause people skip because the pump is obviously running.

Sudden, on a machine that worked yesterday. A blockage — disposal, hose, sump or filter, in that order of ease.

All clear and it still will not pump out. Now it is the drain pump, and that is a repair. We are not publishing a part number for it: pumps differ across model families and the route to the right one is your model number, on a sticker on the edge of the door, through a parts retailer’s fitment tool. Everything above costs nothing, and between them they account for most of these.