My skimmer has two holes in the bottom. One that has the plumbing hooked up that goes to the pump. In that one I put a gizmo in it for the winter. The second hole is not used. For this hole, should I leave it unplugged to allow the water to drain out of it over the winter, or should I keep it plugged and put some anti-freeze in it. I have dropped the water level about 3 inches below the skimmer.