Sorry for the reply to such an old message.
Here is my question:
I just had my inground pool winterized. I noticed my skimmer has 2 pipes. One they blew out and has one of those blue things screwed into it. The other one I'm not sure what it is for. It is filled with water and I am concerned about freezing. Before I call the company who closed it and asked. I was wondering if I could get your opinion on this. I was going to buy some pool antifreeze and drop it in the skimmer (i assumed they already did) but more peace of mind for me.
Anyhow, any ideas what that could be for based on the information I have? Pool level is about 18inches off patio level right now (lower than skimmer.) pipe in skimmer has water but isn't flooding into the skimmer, its staying where it is.