Wow I am surprised it did not have a single return on one side and a single over flow on the other. It seems to be open between each compartment is that correct?
I would come out of each overflow to a larger single drain pipe. I would break up the return to 4 with a ball valve for each return to regulate the flow through each.
I would come out of each overflow to a larger single drain pipe. I would break up the return to 4 with a ball valve for each return to regulate the flow through each.