I know that this isn't a new idea and lots of people use sprayers for showers etc., but I thought I would add my experience to the record.
I got a 1.5 gal deck and masonry sprayer from HD. It was in the paint department not the garden section.
http://www.homedepot.com/p/RL-Flo-Maste ... /100637818
What a handy little bugger to have around. I modified it by lengthening the spray hose and shortening the wand sprayer. I got my extra poly hose and barb fittings from State Trailer.
The nice thing about the deck sprayers is that they deliver a flat fan shaped spray pattern. I know that you can put a sink sprayer on it, but I wanted it to use less water than that. So I kept the wand, just shortened it. Pump it up and it's good to go for quite awhile. Set it in the sun, and it can get quite hot. Or just put hot water in it for a nice shower.
Additional Uses: I put a long hose on it so I don't even have to move it to use it for a zillion things outside the cargo trailer. I can pull the hose out the door of the camper and wash my muddy boots and waders off. The same goes for my hands and even cleaning the odd fish or two. I use it to rinse out and wash dishes. Spraying off grubby grandkids' assorted toys, boots, and hands. It even helps with keeping the porti-potti clean and "fully flushed".
A great $10 investment in easy camp clean.