To save a lot of problem with the return line and which tank to send it to, just dump the returned fuel back into the feed line by the tanks. It will recirculate the fuel without filling either tank, and being back away from the pump, it should have time to cool off.
I like that idea a lot.
Not only does it prevent fuel overflow into the vent line possibilities, it would also prevent aeration of return gas splattering down into a tank, and save me the trouble of haphazardly tapping an NPT fitting into my sender flange.
Return to the feed line would make me inclined to add a heat exchanger on the return line...
Perhaps something like this mounted in front of the radiator:
https://www.summitracing.com/parts/der-13225/overview/My otherwise stock K3500 diesel has an aftermarket auxiliary tank. Electric 6 port selector valve shifts both the supply and return to the tank you select.
Sounds like a solid setup. For now I'm hoping to get away with less fuel lines... though it seems like I'm planning more each day now!
