I am trying to remove fuel pickup tube. Does the fitting just unscrew? I can rotate the large nut. When I turn the fitting, holding the large nut, it rotates but doesn’t seem to be unscrewing. I actually unscrewed the large nut all the way off the fitting and then tried unscrewing the fitting. Same result, it moves but doesn’t seem to be getting any more loose. Can I just install another fitting next to it? What is on the inside of the tank? Is there a threaded fitting built into the tank? Thanks for any help.