I need to connect 5 gallon propane tank line to burner line on hotdog cart ... what should I use on thread ?Plummers Paste , Plummers dope , or Teflon tape ? (Male to female)
If you are using the standard propane fittings and adapters, nothing else should be needed. Not tape, dope, paste, nor putty.
If it's a compression fitting with tapered cone end, nothing should be used. If it's a threaded pipe fitting, either dope or Teflon tape is fine. If you go with tape be sure to use the thicker Teflon tape that is rated for gas, it's yellow not white.
Myself I prefer dope. One decent brand is rectoseal. Type 5 doesn't harden, so it can be changed easily.