Fuel tank

Yeah, duct tape would be my first choice there Red Green!

That really depends on the location or type of leak. There is a way to fix a small puncture providing you have access to the spot. But I would suspect that given the age of the car, which by the way is really all that old, your problem is more of a corrosion/rust problem possibly along a strap that holds the tank on or along a seam.

With that kind of leak, the only way to stop it is to replace the tank. I'd sell you mine very cheap as I am hauling it to the salvage yard because the front end got hit. Not worth it probably so look up used tanks on the car parts hotline and find someone that tests there used tanks or buy a new one.