While there are several reasons a dishwasher does not drain, many are simple, such as a clogged sink drain. If water does not drain from a sink, the dishwasher does not empty. In kitchens equipped with a garbage disposal, the solution is sometimes as simple as operating the disposal to clear the drain.
A clogged air gap prevents the dishwasher from draining properly. Sometimes the water remains in the bottom of the dishwasher, and other times it sprays through the air gap onto the countertop. Cleaning the air gap usually resolves the problem.
Food and grease sometimes collect in the drain connection on the air gap. With the drain hose removed, a screwdriver allows the owner to clean this opening. While the hose is disconnected, one should inspect it for a blockage as well.
The blockage is sometimes inside the dishwasher. Small bits of plastic or food debris sometimes clog the machine's sump basket, preventing water from flowing into the drain. SFGate.com recommends using the end of a wire coat hanger to help remove materials from the sump before removing the screws and screen for a more thorough cleaning.
If the drain path is clear, the water in the bottom of the machine sometimes indicates a malfunction of the pump. Older models sometimes use a belt drive, but newer ones have direct drive pumps. Replacement parts for either type are available.