The idea of using LP Rev. Osmosis rinse water from a car wash is very interesting......I'll keep it in mind.
We camp a lot (tent trailer), so I often bring a large RubberMaid "Blue Tote" and rinse my gear in it using a hose and the campground water. The wetsuit and most of the personal gear gets sloshed around a bit, then I change the water and let the gear soak again for a half hour or so before taking it out to dry on a lawn chair I use as a rack.
The regulator, with the first stage capped, gets put in alone. I slosh it (1st stage is well agitated and the 2nd's are more gently treated so as not push the purge valves). I change the water, then let the rig soak from 30 minutes to several hours.
I do the same with my Nikonos V , SB105 and accesories, sometimes soaking them overnight.
Soaking is preferable to rinsing, btw, as it allows water to penetrate and dilute away the salt water droplets. Salt crystals (precipitates) WILL NOT dissolve once they come out of solution and weld themselves to your gear, so soaking only gets rid of the salt water. If you get some problematic crystallization, it will take a more thorough disassembly and cleaning to get things right. (But, more often than not, you will have some small amount of these deposits present at your annual, no matter how much soaking you do.).
One way of preventing precipitation of salt and other minerals on your gear, especially on long or multiday trips is to keep the gear wet, even if it is with salt water.
I sometimes place a wet towel over my setup in the rack and I place my camera in a "wet bag" under a soaked towel and out of the sun.
So far, 15 yrs. and no camera floods (now I went and jinxed things, didn't I?).