Well I think I spoke too soon. My SWG was complaining about high salt. So tonight I vacuumed to waste and just let the vac run to drain it down some. I am refilling now. While that was going on I investigated the leak. I -think- it's leaking around the threads to the 1.5" PVC fitting that connects to the line to the filter and not the gaskets. Also please confirm but my memory (and youtube) say that the return fitting is threaded all the way through on the ID for 1.5" male PVC threads. I should be able to screw my capped PVC plug that I use for winterizing to the inside, disconnect the union from the outside and screw the return line in more tightly without losing any water, correct?
I was going to say, based on what you told
@duraleigh about it getting worse with the filter on, and becoming a spray when you cover the return that the bulkhead fitting itself is not leaking, it is the connection between the hose and the fitting that needs to be addressed
Yes, you are correct. You should be able to remove the eyeball retaining ring, and eyeball from the inside and put in your winterizing plug in. Take a look here -
Waterway Vinyl Liner Return Fittings Parts - INYOPools.com at the exploded diagram
You are going to remove part #6 from inside your pool and replace it with a plug
Part 5 is where it gets slightly tricky. Part 5 in that picture is a hose adaptor. It threads into the inside of the return fitting and a filter return hose gets clamped to it. That is if you have hoses. You mentioned threads and a union, so maybe you do not have hoses but have hard pipe threaded into it. So you need to remove whatever you have that is threaded into the rear end of the return fitting.
Either way, those threads are NPT threads National Pipe TAPER. The taper here is important. People tend to get all happy about PTFE tape or thread sealant and use it way too much, but in the case of T threads, the threads are doing the sealing, and tape or sealant (or depending on who you talk to, both) are necessary for a watertight seal. Put your plug in, remove whatever is going into those threads (back up your fitting so you don't unscrew the return) look for chowedered threads, and if they are OK, apply tape or sealant and reassemble. 2-3 thickness of tape is fine. Wrap too much and then crank down when tightening and you will be posting about how to repair a cracked fitting.
And when reassembling your union, no tape on those threads, they are not tapered and do not seal anything. However, some silicone grease on the O-ring inside would be nice.