Fuel tank removal

[Ulenran]

Hi all, new t-bird owner here. I have a 79 thunderbird with rust and varnish in the fuel lines from sitting, and im currently trying to remove the fuel tank to clean it. My main problem is that the fuel filler pipe doesnt seem to want to disconnect from the tank, or come apart at any point in its length. How do I fully remove the tank and filler neck?