I have a question about a Propane tank I had filled. I watched the guy fill it. It was empty and he put 4 gallons in. When I picked it up it much lighter than I expected. I mentioned it to him and ...
How old is the regulator? Have you performed any leak check?
Maybe he under filled. I would try to assume he put in 4 gallons and you paid for 4 gallons. Go to a real propane dealer and explain your concerns in advance.