This is a good thread. Just wanted to add my 2 cents. Like others have said. It depends on you and what you feel you need.
We like to be clean and take showers. Usually when we go camping for a week, the grey fills up fast because of our habbits. As well, there have been plenty of weekend trips where the grey has filled up too fast from showering. (Lots of sweating, getting dirty while playing in woods, etc...) Drove me crazy.
We went camping with a buddy who had a 12g tote. He uses it just for his grey. He let me borrow it and it worked great. Is it perfect? No. Do I care? No. Can I put it in my truck by myself? Yes! I just purchased one. It will get plenty of use and I will care a little less about how much water the wife uses now. (Until she starts filling the campers grey tank daily :W)
Usually the black will make it through a week. (Its only two of us.) Would I use it for my black? Hmmmmm... I'm not sure. I may just drag the camper to the dump station then to do both tanks. I'll never say never. It can be cleaned out. (Its funny, makes me think of when we first bought the camper. We said no #2 in the camper. That rule was broken on the first camping trip. :B )
I probably could have got a 18-25 gallon portable and just drag it around to my hitch. For me I don't want to do that. 12g at 96+ pounds, if full, is enough to drag through leaves, brush, and stumps.
