Citric acid. Fill up the dispenser with the powder. It's a trick to clean the dishwasher (told us by our appliance repairman). Every couple of months or so; you'll get to know. Followed by one full wash with no soap.
Years of melted grease are trapped in the drain, etc. Now the inside of our dishwasher looks like a new dishwasher.
An interesting byproduct is that we put those "filmy" wine glasses in at the same time. Filmy stuff is greatly reduced.