Nice table man. I use a lot of PVC for various things like humidity domes, aero cloner manifolds, and things like that. This summer, I had a big Swazi plant, and had the idea to build a sliding frame for it, and I think the same concept could be used to make your table adjustable, but you’d have to rebuilt it I think.
At each corner is a 1", 4 way elbow.
The little nub you see coming out of the 4 way in the closeup, is a 3/4 pipe union. The PVC you use for the vertical rails has to be smaller than the 4 way, so it’ll slide. I had a bunch of 3/4" PVC that I was gonna use for the rails, but 1" 4 ways were a problem, and I didn’t want to buy 1" PVC for those.
I had a bunch of those 3/4" unions, and they looked close to an inch, so I tried them. I was kind of amazed, but they fit into the 1" holes almost perfectly. So, you glue those into the horizontal, “elbow” holes in the 4 way.
For the side legs, where you’re using a tee, you’d use a 1" 5 way:
They’re configured the same way, with the 3/4" unions glued into the tee holes on the 5 way for the side rails, and crossbraces.
I found the easiest way to control the adjustment is to drill holes through your PVC “legs”, at what ever interval of adjustment you want, and use bolts to block the 4 way as it slides down the leg, or you can drill through the 4 way, and leg both, and pin it. Your legs have to as tall as your desired max adjustment height, I think you wanted a 12" max, so that’s no problem.
Hell, if you had a shitload of ratchet hangers, you could probably raise and lower it with those. Sorry for the long-winded oration. I have a hard time explaining shit like this, so I tend to go overboard.
Anyway, I hope this helps you get where you’re going. If you have any questions, let me know.