My son and I closed our 42000 IG pool today. I have a vinyl liner and water goes to the filter through 2 skimmers, I have no lower drains. One of my skimmers has a normal inlet that runs to the pump and another hole, same size , same threaded fittings, but not connected to the pump, just goes down 2 ft and through the pool wall back into the pool. What is this tube for and do I need to winterize it. It's outlet is ver low and I cant see a way to blow it out. Anyone help out? Thanks