One of the holes in the bottom of the skimmer is most likely plumbed to your bottom drain (the one that doesn't generate suction when the pump is on). I believe that some suction occurs at the bottom drain as a function of the suction at the hole plumbed to the pump. On occasion I've sealed the skimmer off with a tupperware lid so that all suction was directed to the bottom drain, then used my pool brush to direct junk to it (sand actually, that my toddler threw in the pool). Other wise it doesn't seem to have enough suction to be functional.