How to properly plumb a tank?

[lastlight]

I never bother leaving pipe gaps but this is good advice. I don't bother with unions but I do buy schedule 80 true union ball valves. they'll turn smoother much longer than the crappy white guys and you can disconnect the plumbing where the valve is.

When do you really need to disconnect everything? If you want to do so make sure you're able to turn the entire lower leg of plumbing otherwise the threaded connection won't be much good.