First try on pressure testing the tanks didn't go so well.
Attached the hardware, sealed the filler cap, and attached a ballon to the vent line. Started pumping. The ballon inflated a tiny bit then stopped. There was air leaking around the schrader valve fitting in the drain valve. So I tightened it with a wrench. Big mistake.
A couple pumps and nothing. No movement on the balloon. Another pump. Balloon went from zero to two feet long instantly and shot off across the room. Fudge.
Then I tried to remove the schrader valve. I had tightened it enough to strip the end.
Checked the threads on the drain fitting and they look fine. Ordered two more test kits and will try again when they arrive.