Blowing out lines in old Anthony pool

[NovaCurls]

Greetings all,
We're half way through closing our 18,000 gal inground pool here in southern PA. Water levels dropped, blew out & plugged returns, but got seriously stuck at the skimmer/main drain. We have no valves besides the multiport, and the skimmer is NOT a two port deal with a flow diverter plate, but one port with a tube diverter (see "Old Style Anthony Skimmer" http://blog.poolcenter.com/article.aspx?articleid=6327). I can connect a shop vac to the tube in the skimmer and blow out all the returns, and skimmer at the pump pad, but once everything else is closed, no bubbles from the floor drain The pool came with the double rubber stopper, so even if I could force air through, I'd have to shut off the vac, unscrew the diverter, and then slam the rubber stopper in. Any advice?
Here's our setup, to my knowledge (just bought the house):
Anthony 18,000 gal plaster pool, 8 ft deep end, installed in 1986
Main drain and one skimmer, connected as described above
2 returns, ~2 feet below coping (can't drain below them unfortunately)
booster return for Polaris
drain/skimmer goes to main pump, a new Pentair variable speed
that goes to the MPV, then a Pentair DE filter, and back to returns, with the boost pump feeding from the return line.
Our property (and thus the pool) is on a pretty significant grade, so I'm definitely concerned about the frost line. Any advice is greatly appreciated!

 

[Bama Rambler]

Welcoem to TFP.

Set the multiport to waste and blow backwards from the waste port to the skimmer and once it's blowing air out (and with the blower still running), plug the skimmer and let it blow the main drain(s) until they bubble. Then with the blower still running set the multiport to closed. That will blow both items and trap the piping full of air. The biggest drawback to that, is that if you plan on removing the pump and/or filter you'll lose air lock.

In that case you're better off installing a valve in the suction line the blowing like above except then you can blow it from the pump suction port.

 

[weird_tolkienish_f]

My understanding is that you only need to drop the main drain 5 feet or so, it only need a few feet of antifreeze at the frost line. No need to completely drain. Actual you can keep pouring antifreeze in until you see it come out of the main drain on the bottom of your pool. What's more, I found out last year that if I pour antifreeze in my skimmer with the pool level lowered (i have a gunite pool with tiles at the water line), the entire skimmer will empty when you pour antifreeze in it. My guess is because the antifreeze weighs more than water?