I made one of those years ago when I was boating. I used a garden sprayer and a hand held shower head with shut-off. As I recall the two parts fit together without any problem. IRRC I removed the hose from the garden sprayer and attached the hose on the shower head with a hose clamp. If you have two different hose diameters, you should be able to find a barbed hose adapter at a good hardware store. I could get a nice Navy shower with one tea kettle full of water heated to "shower temperature" on the stove. Good luck!
