Fuel Leak Help

[TKCR]

Just got my 86 C10 SWB out of the garage yesterday. It has been sitting for a couple of years, in the garage in a dry controlled environment. When I started it up, it started with just a small drip on the passenger side, back where the tank is. Drove it around the neighborhood and pulled back in the driveway. It now has a steady stream of fuel, leaking. It stopped after a few minutes of the truck being off.
What I don't understand, I am driving off the driver's side tank. Are the fuel lines not separated, from tank to tank? Or should I say, side to side? Is there a way I can get the passenger side to completely shut off from the fuel? I need to take it and get it fixed, but the fuel is dripping to close to the exhaust, for my liking.