i have a gas 97 f250 4x4 and the gas is backing up the front tank. what would cause this?

thanks, its a start. from what else ive been reading that seems like it could be it. but im by no means a mechanic, so all the advice i can get helps. thanks

I have a 1996 f250 with duel tanks. I also had the same problem. I replaced the rear tank this summer and was only going to use the rear as the front tanks pump went out. Well shortly after the fix, I noticed the gas Gage moving downward towards E as I drove for 20 miles. Well, the front tank begain to fill up. Soon the rear tank was empty and the front tank was full. The fix. I pulled the front tank and connected the lines together using the metal fittings from the old pump and a piece of 5/8 high pressure gas line rubber hose and clamps. Works great. Started up and runs fine. Hope this helps.