I'm still a little confused. Seems like you have 2 issues that are not related.
Agree
1) You have a leak around the Tee fitting where the flex goes into the fitting. This is a simple glued joint and not a union fitting. This is unrelated to the union issue you describe, correct? Yes unrelated. This is the main problem. I see two solutions. First, seal the leak. Second is replace the flexible with PVC.
This is most likely caused by not properly cleaning and priming the pipe and fitting before gluing. Did you use cleaner and primer before gluing? Yes I did prime and used regular clear PVC glue that I got from home depot. I recall it required me to hold it a long time - not like regular pvc - to get it to stick. It did not leak until yesterday when I took the hose off the pump and filter to do some maintenance. When I put it back on I am getting a drip out of one of the joints between the T and the hose.
2)
I'm still unsure here too. Are you saying that the black unions you show in the picture are leaking around the threads? No they are not leaking. I am saying that they are glued to the flexible hose so I can not use them with regular pvc to replace the hose.
2 inch is 2 inch so i'm not sure whats going on here. Did you use any teflon tape or pipie dope before you screwed on the unions? No i did not use tape, but they are not leaking. They have a plastic washer that seals them.
Also, these look like ABS fittings and not PVC. Are you sure they are PVC and not ABS or even CPVC? If the male threads on the filter/pump are of one type of plastic and the female unions are of another, they might not fit as well. I do not know what the unions or the flexible hose is made of. I found a WaterWay replacement hose with union fittings online, but it is $50 and if I am going to replace the hose I would prefer to use Schedule 40 pvc it I can find replacement unions.
I'm just guessing here. Also, did you buy the male and female pieces together, or were the male ends already there? Did this work at one time? Yes it all worked fine.
Sorry for all the questions, but sometimes it takes a bit to go back and forth to try and understand just what the issues are. Be patient