So, we were told by the pool builder to plug our fill line for the winter -- the fill line feeds into the pool, under the water line. They said to use a shop vac or air compressor or something to blow air into the line and then put a plug (which we were given) into the hole where the water comes out, under the water. We think we did this last night, meaning, my husband blew air into it using a shop vac and I saw bubbles come out into the water, and then I put the plug into the hole. My question is -- since the hole is underwater, there is pretty much no way it was completely free of water -- is that okay? I mean, some water probably got pushed back in or trapped when I was putting the plug in. I am just not understanding this concept. Are we actually worse off now in that any lingering amount of water in the fill line is going to be colder than the water in the pool, because it is no longer in contact with the water in the pool, and thus MORE likely to freeze? Does this make any sense?