Normally when I close an inground pool, I blow the lines and plug them. If the line is properly blown, there is no water to freeze.
I have a customer that wants me to add Antifreeze to their lines. I have no problem with giving them what they ask for, but I just don't see what value this adds. From what I have seen, most people just pour a gallon or two into the piping. I don't see how that is going to do anything. Unless you pour in enough that it runs through from one end to the other, you have no way of knowing if the antifreeze is going to help.
To me, it would make more sense to first blow the lines. Then fill the pump basket with antifreeze and blow the line again so that the antifreeze is forced all the way through that line to the pool, then plug the line. At least this way you can be reasonably sure that the antifreeze made contact with any water that might still be in the line, and would have mixed with it to prevent freezing.
Am I missing something when it comes to pouring the antifreeze in? It just feels like something else to sell pool owners that really doesn't offer too much real protection beyond what is already there from blowing the line. If the antifreeze doesn't fill the entire pipe, its entirely possible to have low spots full of water that might still freeze.