We use three of the garden pressure sprayers. One for showering, one for spraying dishes and the third for the toilet.
The one for showering has a two gallon stainless steel pressure tank. That way the temperature of the water can be tested through the metal as you are filling the tank. The other two are cheaper plastic types. On each one I shortened the hose to just the needed length.
We use a two-gallon plastic one for the porta-potty. With it you can direct the spray where needed such that it takes much less water than the built-in flush on the porta-potty. Also, I mix a light
concentration of the potty chemicals in the sprayer water. It seems to freshen the air a little and also seems to do a better job of cleaning the bowl. I also make sure a little bit of rince water is left in the bowl after shutting the valve - approx 1/2 inch. It lubes the gasket for the next use. Also, since there is no water in the upper tank of the porta-potty, it is easier to disassemble for dumping.
For the dish sprayer, we add about a tablespoon of bleach per fill-up of rince water. Then we collect the rince water as we rince and use it next time for wash water, since it already has a bit of detergent and bleach in it. The dish sprayer has a smaller one-gallon plastic tank.
I'm glad to see that there are others out there that put garden sprayers to use in their RV living.