Directly to the question, I have a 12 I think anyway it is the small size that they all make and the cheapest. We bought some property and park it there for a better part of the summer. I have used the portable tank 4 times. I took my time and went slow. It is very doable. This size tank is heavy when it is full. Too our surprise, It seemed to old pretty much the full black tank. We sit on the grey for finale flushing of the black. We had a pop up for twenty years and finally bought a trailer. We are very used to conserving water. Dare I say, most of the time we go number one outside and when it gets late, inside. The list goes on and on, but we are used to it. I would not buy anything bigger than the small size, more in line with your capacities anyway.