Remove all dishes from the dishwasher. Pull the dish racks out as far as they will go to open up the unit.
Locate the drain in the dishwasher, which is typically at the bottom. Refer to your dishwasher user's guide for complete instructions on where the drain is. You may need tools to remove the drain cover. Most newer dishwashers have a cover that twists off, while some are bolted in place. Remove the cover to expose the inside of the drain. Put on rubber gloves, and clean out any bits and pieces of food by hand. Alternatively, use a plastic spoon.
Wipe up debris from the inside of the dishwasher, using clean paper towels.
Start the dishwasher’s cycle, and wait until the bottom is full of water. Pour in 2 cups of vinegar into the water, and allow it to sit for 30 minutes. This will help to remove any hard-water buildup.
Scrub the inside of the dishwasher, using a stiff-bristled scrub brush. Make sure you get corners and other spots where grease and food can buildup can be especially heavy.
Restart the dishwasher, and allow it to finish the cycle before you use it again.