I have just installed a AO smith gas water heater. All my water lines are 3/4 inch copper. The Tank came with 2 dielectric close nipples with no mention in the installation instructions.

My old tank of 15 years had the copper 3/4 male fitting screwed directly into the top of the tank with no problems.

Question : Should I now use the nipples directly into the top of the new tank and then get a female copper fitting to screw directly onto the nipples or should I just thread the male copper fitting into the tank like it was in the previous install and throw the nipples away?

A web search shows installs both ways.