Oh ok, not the union itself, I see.
And yes, FWIW I agree, hand-tightening bulkheads should be all you need.
I was just saying, you can crack glass by overtightening those.
However ....
You can still crack open a FNPT to MNPT connection if you overtighten. I was doing the exact same thing as you about a week ago on 1.5" pipe, I just used a pipe wrench, and that "extra 1/4 turn" was all it needed to crack open. Just sharing some experiences... trust me I've found lots of creative ways to break things.