When everything is hooked up I have a feeling that there is enough pressure in the injector return line to make the flow go in the correct direction. If you just unplug the line from the banjo bolt the fuel will naturally take the easiest route (the open hole)

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine