Never had an order issue. When we dump our tanks we flush them until the water runs clear, close them and add a gallon or two of water plus the tank treatment (I put a a little in the gray tank also). We keep the black tank closed while in camp and the gray tank open until the night before we leave then we close the gray tank (I know some folks do not do this with the gray tank but we've never had a problem). We've always used Thetford Campa chem - love it. Campa-Chem® Original | Products | Thetford