help with idea for PVC on pool for winterizing

Sorry, I know this isn't exactly plumbing related to inside a house but I have an issue with my inground pool plumbing when I'm trying to winterize it.
We bought this house from someone a few years ago (short sale) and evidently they didn't winterize it well enough which led to a cracked line. Our pool has two lines running to the pump. One from the skimmer box and one from the bottom of the pool. They are both dedicated lines and both need to be blown out and sealed at the end of each season.

I've fixed the crack issue (fortunately it occured right below the concrete patio where I thought it was so I lucked out there.)

Two years later though, that lower line is a pain to clear and keep air tight. As shown in image at the pump there is a ball/union valve for this dedicated line. I've replaced all the rings and washers once already because the original stuff was all scratched up and wouldn't hold air. I already notice after one season small scratches on the ball surface and worry it will let air out over the winter season and recrack the line. I want to come up with a solution that I can rely on and be easier to seal. Currently I open the ball valve, place an air line from compressor into the opening and shut off the valve as quickly as I can once air bubbles start coming from the bottom of the pool drain.

My current thought is to remove the ball valve which leaves me the threaded end of the union which is solvent welded to the line. Then screw on "something" that has a one way valve like a schraeder valve or something so I can fill it with air and not worry about it again. Then just remove this ghetto unit when I open the pool and put it in storage for next year.

Anyone have any ideas on how to do this or any better ideas? I've searched the internet but can't find anything that fits my need.

Not an answer to your question, but all of our neighbors blow out the lines and then dump in some RV antifreeze for insurance.

Yep, blow most of it out and run RV anti-freeze in the lines.

Those union nuts are NOT generic, but sometimes the manufacturer will use the same nuts for his union valve AND regular union. If you can find one then just install a bushing and shraeder valve into it and connect it in place of the valve. If you see "bubbles in the water" that must mean you do NOT drain the pool all the way. Jut curious, but in CT, which day of the year is warm enough to use the pool. I would guess it is around June 21.

thanks guys. I did some research on antifreeze, I wasn't big on the idea of adding it to the system and how to get it out during opening. Plus, what's the purpose of blowing out the line if I have no way of adding antifreeze to it once its blown out without it backfilling with water under pressure on the pool side unless I'm missing something.

Hj, that sounds about what I'd like to do. I guess I just need to find the right threaded union. How would you connect the schraeder to the bushing? can I buy schraeders threaded for PVC or do I need to tap a hole in the pvc and install the schraeder?

I live less than a mile from Long Island Sound so temperatures aren't too extreme come winter. We tend to try and open the pool the weekend before Memorial Day so it's ready by the long weekend. We have a propane heater (came with the house) but I try to use it as minimally as possible. The solar cover does wonders for keeping the heat in once it has heated up the surrounding ground. During a pool season I may use about 100lbs of propane. Hopefully will be able to get a gas line in here soon to at least get cheaper fuel. It kills me heating something like that.

My guess is Arizona has a slightly longer pool season....;)

Buy the proper sized bushing with the smallest reduced side. Then you can step down from there with various sized bushings until you get to the final one which should have be 1/2" with a female thread. Install a 1/2"x1/4" brass bushing into the PVC one and screw the Shraeder into it. One of my customers had a pool installed with a propane heater. They furnished an almost "tank car" sized LP tank for it and his 30 gallon water heater. After they filled the pool they turned it on and lit the heater. The next day they were back with their LP truck. He asked them why they were there and they said because the tank is empty. They refilled it and he NEVER turned the heater on again. Every year the LP company would come to check the tank to see if the water heater had burned off enough gas so they could take the tank back. Another of my friends likes to send out New Year's cards with him swimming in his pool on Jan. 1.