Last Fall I finished up my 95 F150 project by working over the gas tanks. On both tanks I replaced the pump, hanger and sending unit. About a month later I developed a leak from the top of the side tank. I ran the tank dry, and quit using it till I was able to find time to fix it. About a month ago, I remembered the cause of my problem. I had forgotten to connect the rubber hose to the vent valve on top of the tank. So, I hooked it back up, and still didn't use the tank for a couple of weeks. When I finally used it, something strange happened. I wasn't able to fill the side tank. The pump kept clicking off, as if it were topped off. I was able to force $10 into it, and I finally just quit, because because of how long it was taking. At the same time, I topped off my rear tank. When I started driving, gas started gushing out of my rear tank door. When I got to my house I shut off the engine, and gas kept coming out. I removed the cap and gas was coming out of the spout, as if it was being pumped, and the key wasn't even on. This was last weekend. I was going up to my dad's. I drove the truck till it was down to 3/4 tank, and gas was no longer coming out of it, then I switched to my front tank, and ran out what little I got in it, then switch back to the rear tank and emptied it. When I went for a fill up, the side tank started taking fuel. This weekend, I went on another trip. I filled up the rear tank and emptied it first. When I switched to the front tank, the pump would not shut off once pressure built up. The pump just kept running. I flipped the switch back and forth a few times and it finally stopped. So, I started driving. Then, it seemed all of a sudden that I was getting a LOT less gas mileage than the first tank. I ran the tank empty and switched back to the rear tank, and the gauge moved all the way up. So, after such a long story, my front or side fuel pump is continually running, and what the engine isn't using, is being pushed back into my rear tank. And vise versa, when I switch back to the rear tank, it runs the engine, and also deposits fuel back into the side tank. Any solutions???