I closed my pool for the first time this year, using a 6 gal air compressor. I have a variable speed Pentair pump, not one of those that you can manually set to backwash, etc. I'm really confident I blew out the skimmer, returns and deck jets fine, as I got plenty of air flow, etc.

However, with the main drain, I got some bubble but not at the level of the returns. I convinced myself that was fine, since the lines are below the frost line. Then, after taking apart the filter system, I decided to try to use my shop vac to blow the main drain for piece of mind. But no air came out. So now I'm thinking not only is there water, but by opening the valve, I probably brought even more in.

Up all night thinking I should put the darn filter system back together again, just to make sure. The way my pvc are setup, I don't think I can put antifreeze near the filter lines for added piece of mind.

Thoughts on putting it all back together again for the compressor, or should I try the shop vac again? BTW, my filter is not close to the pool, so the lines are pretty long, so more water to push.

Thanks for your thoughts!