Do all dishwashers have a filter that has to be cleaned?

Not all dishwashers have a filter that has to be manually cleaned, it depends on whether the dishwasher has a manual clean filter or a self-cleaning filter system. Modern dishwashers manufactured after 2010 including most Whirlpool, Maytag, KitchenAid, Bosch, GE, and Miele models have manual clean filters located at bottom of tub under lower spray arm that need to be cleaned every 30 to 60 days. These filters consist of coarse outer filter and fine mesh inner filter that trap food particles to protect pump, and if not cleaned, cause poor cleaning, odor, and drain clogs. Older dishwashers manufactured before 2010 and some budget Frigidaire and older GE models have self-cleaning filters with a hard food disposer that grinds food particles and flushes them down drain, similar to garbage disposal, and do not have a user-removable filter that needs regular cleaning, though they are louder. Some high-end Bosch models have self-cleaning microfiltration that rarely needs cleaning. So if your dishwasher is older and you cannot find a cylindrical filter at bottom after removing lower rack, it likely has self-cleaning system that does not require manual cleaning. Check your manual by entering model number at manufacturer website. Even self-cleaning models benefit from occasional cleaning of spray arm holes and running Affresh cleaner monthly. Manual filter models must be cleaned to maintain performance.