Every week I remove each pan from the rack, scoop out all the mice into a holding bin, dump the dirty litter, scrape the pan out with a putty knife, replace with fresh litter and move the mice back in. I don't even wash the pans and haven't in years. Mice live in a world of scent, they need their homes to smell familiar otherwise they don't feel as comfortable. I've found that if I wash the pans they actually smell worse after a few days because the mice will be extra busy re-marking their territory.