I am a pool novice, so take this for what it's worth, but hope it might help.

Our 1975 era pool has return jets with pvc fittings (eyeball style, with a re-positionable middle part and a ring that screws down over it). When they closed our pool, they unscrewed these fittings and replaced them with rubber plugs. Looked like the attached link...

As far as how this works into your particular pool closing, I don't know enough about it to say, but just fyi with what I've seen!

Here is a link that might be useful:

Fittings for returns must be removed first. The rubber plugs MIAOkc referred to are put in and tightened/sealed as air is blowing out fast enough to prevent water from coming in.

A compressor provides high pressure but low volumes. A blower or high powered shop vac in reverse will provide high volume at a lower but acceptable pressure and should be used.

Bottom drains are air locked while being blown. As long as any water in the pipe is below the frost line, it'll be fine. If you hear air hissing when locking the drain, the valve is leaking and a winter plug should be put in the pump to seal the air in the pipe.

Scott