Wasting water waiting for hot water???

Simply tee into a hot water line as close to the shower as possible, under the sink may be good. Add a valve after the tee and run this line to the fresh water tank fill.

Open the valve till hot water reaches it. Close the valve. Done.

My technique is to brush my teeth immediately before my shower, using the hot water valve at the faucet. (Not leaving it running...just as needed). This will usually kill a half gallon and purge most of the cold without waste

In a stick & brick with the water heater in the basement and with kitchen and bath on main floor, you don't need a pump. All you need to do is tee into the hot water line at the farthest point from the water heater. Then run a return line from that tee to the bottom of the water heater. The water will thermosiphon back to the water heater.
Would this work in a RV ? Good question, I think it would, but not as well as it does in a home with the water heater in the basement.

Steve, Your design using a 555 timer is brilliant! Wish we could see a design drawing of how you actually did it. Sounds like a perfect solution.

Ya I don't know why simple 12v RV recirculator isn't offered. We added one to house, 35' run to bathroom sink, waiting waste was in gallons.

Camper maybe quart to 1/2 gal-but that's every time you'd like warm water. I get caught up in the details every time I think I'm going to address camper. Started a couple of times. Simplest is just another line back to tank. For some reason don't like the idea, though many do.
Id like to see recirc thru water heater via its cold inlet which involves 2-3 check valves. I actually picked up small pump but haven't pursued- mostly finding small check valves. Or tee with with 2 checked inlets.

What I do not know is if simply pumping hot to cold line at sink would work. Other wise seems small pump between with single check valve. Use thermal button (w/manual switched power)or simple momentary switch to control. I 'think' the flow would be loop side thru water heater and not involve main pump, not sure.

Hmmm I have flex lines on bath faucet now, lines are tee'd for shower valve. Simplify playing with it, 'least enough to see if this viable.... umm also have second water pump switch in bath, tap that to energize recirc pump switch...
Think Ill look at it tomorrow or at least think about it.

I never worry about a few ounces of water lost while waiting on warm water. I have a 100 gallon fresh water tank, pair of 7.5 gallon tanks that I sometimes fill while out sightseeing.

As for 'conserving water' - what I will do while dry camping (if I really want to stay someplace more than 2 weeks) is scoop up some of the grey water from my tub (while showering) and put that into a 1 gallon jug to use as flush water, or if I am concerned about overfilling my limited 42 gallon grey tank, I can put more water into my 59 gallon black tank.

Many times while camped in the desert, away from other campers, is dig a hole, and let much of my grey water into that hole, so the local plants can get a drink. But never try this in a 'established campground', especially a state or federal campground.

Fred.

What I do is turn the WH on 15 mins before I need to take a shower in summer and 25 mins in the late fall. I just use the hot water facet that way there is no adjusting to be done. I always run out of water before battery and try to conserve as best I can while dry camping.

I did something similar to smkettner, but without the extra pump.
At the galley sink (the furthest fixture from the water heater), I installed a solenoid valve that drains the hot water back into the fresh water tank (via the inlet hose of the water pump ... which just happens to be located under the galley sink). The valve is controlled by a switch that is connected to a simple timer (555) that maintains contact for a predetermined amount of time. When we want hot water, we just push the button (conveniently located right at the galley sink) and in about 20 seconds the water is hot. The timer opens the valve after about 45 seconds and the main water pump stops soon thereafter. Before a shower, we also push the button. The system can also be set to automatically run whenever the hot line temp (at the galley sink) drops below 95 degrees, but I seldom use this feature because I don't like leaving the water pump switch on...an advantage to smkettner's system.

double post

We capture about 1/2 a gallon before the water is hot at the shower. We then pour it into our Berkey traveler water filter.