I’m trying to drain my pool 6 inches below jets , it’s below the skimmer now ( I have sand filter with waste line) , skimmer is now off and water should be draining via bottom drain - it appeared to be working very slowly ( I could hear water coming out of waste pipe but it seemed to not be lowering the water after an hour). Then I checked on the pump and there was no more water pouring in so I shut it off. What am I missing why is going so slow and then stopping to work?