$24 gets you one of these, they work.
Use it while standing in a plastic tub filled with water adn recycle the water...
I have used one of those for the past few years. The problem is that the pump always eventually fails. As mentioned previously on this forum, when my last one died i threw the pump away but kept the showerhead and bought a bilge pump for it. I re-used the cig plug, cable and waterproof switch too. Works great!
* Cheap camping store shower which had died anyway $25
* 1 metre of clear 3/4" tube $1.25
* Plastic elbow from local plumber's $1.15
* Plastic hose size adaptor from local plumber's $1.00
* 3x 3/4" plastic clamps $0.80 (20 cents each) from local plumber's
* 1x 1/2" plastic clamp $0.20 from local plumber's
* Waterproof fuse holder & crimps $6
* Bilge pump $35
Proved it's worth last weekend at an offroad motorcycle comp i competed at last weekend. When the showers at the location went stone cold and my wife and kids wanted a shower after a dusty day it took me all of 10 minutes to setup the toilet/shower tent, camp shower and boil 2-3 kettles for a nice warm to hot shower. 1 jerrycan does 2-3 of us.
cheers