That depends. If floating objects like leaves, twigs, mulch chips, etc. have fallen in, then overfill the Ollas until these objects float to the surface. Then skim them off. If dirt and debris sinks to the bottom of the Olla, than the best way to clean it is to remove the Olla from the ground and wash it out with a garden hose. While you’re at it, use a scrub brush on the outside to clean any dirt and debris.If you have water that is high in mineral content (like calcium here in Tucson) then cleaning your Ollas with a vinegar and water solution is highly recommended. If you want to know when to do it, take a peek inside using a flashlight (when the Olla is empty). If you see evidence of white chips in the bottom or a white lining on the inside walls, then it’s time to clean.To begin, pop the Olla out of the ground. Clean any debris that might have collected inside. Then mix up a 1:1 vinegar to water solution and pour it into the Olla. Fill it at least to where the neck enters the pot. With the Olla propped up vertically, let the solution do its work. Plan on a wait time of a few hours. Then properly dispose of the water/vinegar solution. And finally, wash the interior of the Olla out with fresh water before burying it in the ground.