I put a quarter cup of white vinegar and alternate each load with a quarter cup of bleach. Mine is 8 years old and looks brand new. They have more complicated "recipes" but, I go the easy route. ;)
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How to Clean Your Dishwasher!
Dishwasher Repair Tips: Dishwasher Not Cleaning Dishes
Want to make your own dishwasher detergent? It is so much less expensive and there are many different ways to make it!
Your dishwasher washes all the food off your dishes. But who washes the dishwasher? You can, by pouring 1 cup of vinegar into the bottom of the tub and running it through a cycle without any dishes. Doing this once every month or two will remove built-up soap residue and keep it in squeaky clean shape.