Useful when dry camping, boondocking, or in a campsite with water but no sewer hookup.
A 12 volt solenoid valve which taps off the hot water line just before it enters the facet. The output of the valve dumps into the fresh water tank. By operating a switch or push button for a few seconds, hot water is pumped up to the faucet so you don't waist fresh water or fill up your gray tank with that water while waiting for hot water to reach the facet.
The same valves can be used on the shower although it is a bit harder to reach the plumbing inside the wall.
Valves can be found on Amazon for between $15 and $50 depending on models and which seller you pick.
Make sure the valves ordered can handle hot water. Some are only certified for cold water. #262524