Closed Pool but found water in skimmer return lines

Hi Everyone,
First time post here. I'll try to be as thorough as possible.

I have an inground pool about 20,000 gallons with a DE filter, 2 skimmers, 3 returns, and a main drain in Lancaster, PA. I closed the pool back in early October by blowing out the lines at the pump/filter and plugging the returns with rubber plugs one at a time. Then I used plastic gizmos in the skimmers - spitting out as much water as I could get out of them. I did not drain the pool below the skimmers - we have a mesh cover. Anyway, I was a little leery about water freezing in the lines so I was going to dump some anti-freeze in the skimmers, opening the gizmos and dumping it straight down into the lines. Today, I went to do that but there was water pretty close to the bottom of the gizmo, I only got about a quarter of the gallon in there, if that.

So I guess I have two questions - what do you think happened? Did I not get the gizmos sealed properly? They are pretty old/brittle and definitely need replaced but I thought I could get through this winter. Is there any other possibility? I did have a tough time sealing all of the returns with rubber expansion plugs but I don't think water could have gone in there and all the way out to the skimmers with the valves shut.

Secondly, what can I do at this point to mitigate the risk of freezing? Can I put the pump back together and pump the lines to waste - then put in new gizmos, add anti-freeze and shut the valves? Should I try to pump the pool water below the skimmer returns? Thanks for any help you can provide.