4r70w transmission rebuild

Hey guys! Im rebuilding my 4r70w due to a burned out forward clutch. I already have all the new seals, Orings, clutchs, and steels installed. Now before i finalize this process Id like to air test each drum to check for proper engagement. From what i understand in order to air test the forward drum you need to install both forward and reverse drums onto the pump.....but i cant figure out which feed hole to hit with my air gun!!!! Can anyone help me?