The fuel lines inside the tank often get brittle and break off. Remove fender pan, remove fuel lines & fittings from tank and inspect. VERY possible reserve line has broken off or strainer is clogged. Bob
The trick to install is you put the whole pickup together with the bushing over the hose between the pickup and the tank fitting. Lubricate with anything except wd-40, seat the bushings in the tank, then press the tank fitting down into the bushing.
You probably want to wash the tank while you’re at it. You can drain 99% of the final rinse water, then one day in the sun will remove the rest.