89 ford F-150, gas tanks

my 89 ford F150 has been sitting for a while and i have kept both fuel tanks almost empty, now im moving and i wanna sell the truck so when i took it to the gas station today to try to put some more gas in the tanks the gas just started to spit out of the tanks. Whats the problem they are acting like they are full?

not sure big but i have a 92 if you need to ck. something.does this act the same with both tanks??i thinking its like you are filling too fast & the pump shuts off?? have you tried slowing down fill rate??if that works it would suggest a blockage... but in both tanks???Good Luck!!

is the flapper opening as it sit awhile and it is likely the flapper is stuck. also there should be vents holes in the fillerneck make sure they are clear.