The pool at the home i just purchased has only one drain line coming from the skimmer port to the pump,then from the pump to the sand filter and then through the chlorine feeder and back to the pool. There is no valve before the pump to switch from skimmer and main drain. The skimmer box does have 2 pipes in it. One might be the main drain pipe--would there be a valve in there i need to open? My understanding is to winterize i need to get the water level below the skimmer and the return ports and then blow out the water in the lines. Any suggestions on how to drain the pool correctly would be greatly appriciated.