After having fluid constantly flowing out from the pressure relief solenoid all over the engine compartment, I decided to have it empty into a container. Since my "fuel" tank was in the back of the truck, I needed to somehow get it back there. What you see here is a universal windshield washer tank from JC Whitney. It holds about a liter of fluid. The hose from the overflow solenoid attaches to a fitting installed to the top of the tank. At the bottom of the tank is a 12v mini-motor designed to pump washer fluid. A hose runs from there to the back of the truck to the "fuel" tank.

In order to have it pump back to the main tank I needed to make some kind of automatic system. The best solution was to use a a float switch to trigger a timer circuit. That solution turned out to be a simple controller used in car alarms called a 528t Pulse Timer. When the fluid rises the float will trip the timer circuit and turn on the pump for an adjustable amount of time. Then, the circuit will time out and shut off the pump. Just fill the tank and adjust for however long it takes to empty the container.

This is the 528T Pulse Timer and wiring in one project box mounted to the firewall.

You absolutely must have a separate fuse block for this system and any other devices you add to your vehicle.  In order to keep this system completely separate from your cars own electrical system, I recommend you install a separate 90 am solenoid.  This works like any other electrical solenoid.   The heavy switching is controlled by applying a small voltage to it from a key-on power source.  When I flip the main power switch, it activates the solenoid and provides power to the whole fuse block and all its components. It's wired with 4ga cable directly from the battery and then 4ga wire to the main buss on the fuse block. This is the best solution that I could find.