My 36x18 IG rectangular pool has 2 main drains in the deep end and 2 skimmer boxes, one in the deep end, one in then shallow end. Over at the pump, there are 2 valves on the suction side, ones for the main drains and one for the skimmer boxes. What ratio of main drain to skimmer box should I be set at. I usually leave the skimmers wide open, then close the main drain for vacuuming.