I am a believer in the KISS method. While I envy those guys that show up in a remote camp with a system tied into their radiator, or a kitchen nozzle coming from their trailer I dont envy them when that stuff breaks at the worst possible time it seems.
So here are my KISS systems. I have used solar showers, spit baths etc over the years. Now I use a handheld bug sprayer, holds about a liter of water. I have used the bigger ones but they take up too much room. I can take a quickie "shower" with this little one using my brought with me warmed up water. Usually do that every other day when on the trail, works fine for me. I need a real shower after a week or so.