My Petter PJ-1 came with a rubber fuel return from the injector bypass output to a bushing at the top of the fuel tank. I have done the same on my newly fabricated power plant in which this engine is now installed. The return flow just goes drip, drip, drip inside the tank. Works great.
I also have a fuel return to tank from the injector on my JD175A engine. It was a cheap clear vinyl type plastic hose that if disconnected at the injector end would drain the fuel tank to some level less than full of the tank was full, not good. Problem is the return enters the fuel tank too far down the sie, not at the top. I replaced the cheap line with a good automotive rubber line, 1/4 inch ID.
When I made the VW plant from a 1980 Rabbit diesel 1.5L NA engine I ran the fuel return from the injector pump to a bushing at the very top of the fuel tank. Can`t seem to recall just now where the overflow manifold hose system on the injectors goes, maybe a port on the injection pump associated with the return discharge to the tank.
Stan, just run a line to drip into the very top of your fuel tank with no drainback valve. Don`t have the end of the line dipped in the fuel or you could create a siphon drain like my JD came with if the line ever comes off the injector or something.