True story from 1976 of all years.
I went to Disney World. On the way down I stopped to help some folks in a Van who were broke down on the side of the road. Got 'em going again NO COST (Should have charged them a pretty girl. Oh well hindsight is 20 20)
They had serious fuel supply issues. They had gone so far as to replace the fuel pump (Waste of money as it turns out)
They had borrowed the van.. The owner had done a DIY aux tank which was located in one of the fenders (The main tank is where you expect it... between the frame rails)
Instead of a "3 way valve) he had two petcock type valves and a "T" fitting
Well with both valves open the Aux tank drained down to the Main tank and then the fuel pump sucked air.. Closed one of the petcocks and VAROOM off they went.
Moral. DO IT RIGHT