We dry camp a lot. The bath is considerable distance from the water heater and a lot of fresh water gets wasted getting the hot there and the grey tank then fills quicker.
What I did was to install a hot water circulating system which returns the cold water in the "hot" line back to the fresh tank.
I installed a tee under the sink hot line and a irrigation control valve with push button at the sink. Ran a line back to the fresh tank. The valves will work on 12v even though they are designed for 24v.
Now when we want to use the shower or sink, hit the button for 5 to 10 seconds and when you turn on the shower/sink, instant hot water and no waste!
