I’ve got to admit something. My family’s wholesale plumbing supply store sold hot water heaters so I knew what parts I needed and learned from my father and our plumber friends how to do it.
I used a mirror (the heater was way back in a corner), a blowtorch, and some good solder. Took me about 15 minutes because I had to hold the mirror in one hand, heat the solder and then drag it around the fittings threads to make a solid bead.
I might even have had a small flashlight in my mouth.
As Blutarsky would say, “Nine years of college didn’t go to waste”.
Blow torch? Heck - mine was all just fittings and stuff. Even bought a new line to connect to the gas valve just “because”.