Gas or diesel toad for this application

[TonyMac]

My father installed a second tank in their gasser, his own invention. When refueling, he'd turn on the refuel switch under the front hood. It would pump gas from the main to the second tank, continuously. Once the second tank was full, it would continue to pump from the main to the second, with overflow coming back into the main. Once the main was full, the nozzle would shut off, he'd shut off the refuel switch, and check the oil since the front hood was up anyway. On the road, the pump would continuously move fuel from the second tank to the main, keeping the main full and overflowing back into the second, till the second tank went empty. Once the second was empty and the main started to deplete, he could see it on the fuel gage.