The filter catches lint, coins, hair ties and the odd stray sock before they can clog the drain pump, and a blocked one is a common cause of bad smells and poor drainage. On most front-load machines, it sits behind a small panel at the bottom front, so keep a shallow tray and an old towel handy, since water will spill out when you open it. Unscrew it slowly, pull out any gunk, rinse it under running water, and screw it back in firmly. Check your manual for the exact spot, as the location varies by brand and model.