Side of the T to the heater, suply in the top, 6" niple to the bottom with a cap on the end. That all goes after the gascoc that shuts the unit off for service.
Ok, you never stated it was natural gas. I assumed it was propane. Around here the propane does the final tie in to the tank and they can be a little picky about how things are done. I just figured they'd complain about no drip leg.