I agree - we have a 21 fresh and 35 grey tanks - go as big as you have room for. If I had my way I would have put a 100+ gallon fresh and greywater tanks and fill/empty them every few days instead of every day. Then use a larger pump system with tanks in the back of my truck. We were at a fixed location most of last season. It is a real pita to have to be there to do the water every day.