Jim, I just reviewed Carl Munroe’s PG book. From the diagrams in the book it looks like the small hole is for suction return and needs to be open. The circuit runs from the sump through the pump, regulator valve and then splits. One side goes to the rest of the system and the other is the suction return which goes to the small hole. Hope this helps. Sorry but haven’t yet figured out how to post pictures on this site from my IPhone.