thats the staple washing method for "urban survival". if you have to save water just wet a towel with hot water and wipe down your entire body starting with your face and ending the the pooper.

look at msr dromedary water bags. they are industrial tuff, black (solar), and can double as a bullet proof water supply. shower adapters come separat, but they are simple (and simple seems to last a lot longer). there are other adapters too...gravity filtration, spigots, etc. it even won the "gear of the year" award in backpacker magazine!

i have the 10 liter bag, and hang it up at base camp. they come in several sizes.

msr dromedary bags

here is the shower adapter...

dromedary shower adapter