After every time I dump my gray water tank, I use 4 of the dishwasher pods of soap. Little dissolving packets. These soaps do not suds up and are designed to cut grease just like they would on your dishes in the dishwasher. As I then fill the tank during use, the soap does it's thing and keeps the grease emulsified so it doesn't collect on any thing. When I drain the gray water tank, I also refill it and flush it once. Then 4 more packets for the next trip and to keep things fresh smelling until then.