I have a 1995 ford F150 that I have own since 97. I have a problem and was wondering if anyone else was having this issue

WhenI fill the rear tank it has to be pumped very slowly. I have been told that the relief valve or line that comes out of the tanks pump assembile needs to be clears out. Is this true? Taking the entire tank out of the truck just to find out tat i is not would suck. Anyone got any ideas what could be causeing the tank to fill so slowly. The truck has never been wreaked or anything, it looks brand new.

Thanks for all your help