After a few tries, I did get all the seepage stopped. I discovered that 1.5" nipples take a lot of teflon tape. I addded more then I modded my DIY wrench for more torque and got the gasket tight enough.
But the o-ring seal surface on the union wasn't flat and smooth. I sanded it flat with 150, 220, and 320 before I was happy, and it sealed with out issue.
In the whole business I drained and refilled 20% TWICE to R&R the valve assy so Felix wasn't happy at all. Not after his recent moves.
But he is healing now, and when the soreness goes he will probably stop hating on me. His appetite is returning. He hasn't been really hungry since all the tank moving, but he is eating a few pellets more each day, and getting more interested in food. He's totally rejected his nightcrawlers, and that was once his favorite.