You must have had a tank with bad threads or a bad regulator. You don't want to use teflon tape on the regulator threads. If a piece of that stuff gets into your regulator you are screwed, and so is the regulator. All that should be needed on the regulator threads is..... nothing. The washer should seal that connection. And did you know there is a permanent brass seal for that connection? It screws into the regulator and has a O ring on it. Works like a champ! All the other connections on my tank use pipe dope. I don't like the idea of the way the teflon tape shreds. It can clog needle valves real easy.