Once in a while we'll stay in a marina with in slip self pumpout. l'lI do a pumpout then bring a garden hose in and spray the tank walls, corners, and bottom through the 6" inspection port in the top of the tank, then do a final pumpout. My tank is translucent plastic so it is easy to see when the crud is gone. I probably wind up doing this every year or 18 month. Steve Willett Monk 36, Gumbo Thibodaux, Louisiana