I have had a smell of gas for the past year or so but never any visible leak or loss in miles per tank. When I got home after filling up yesterday it smelled worse so I looked under and it was dripping. I caught what I could last night which was about a half gallon, the filler hose looks dry that was my first thought. The gas is dripping from all the low points of the plastic skid shield on the drivers side of the tank. I pulled the shield down as much as I could to look and couldn't see any hole but it was obvious leaking down from somewhere between the strap at the forward end of the skid shield and the rear of the tank. The truck still runs normal and drips the same on as off. I am thinking it would have to be the tank but any insight. I tried to get some gas out of the tank to temporarily stop the leak but I cant get a tube down into the gas via the fill.

 

You won't be able to siphon any fuel from the tank, there is an anti-siphon device in the filler tube. Looks like a big ping pong ball between two sheets of metal that have holes in them. Atleast it's in my chevy I'll assume it's in your olds as well. A crafty way I've seen to drain the tank of fuel is hook up to the shcrader valve on the fuel rail and run the car, run that hose on the schrader valve into an appropriate container. An inline shut off valve is a good idea on that tapped line.

Getting back on topic, this happened to me a few years back, and the wall of my tank was corroded away by road salt. The leak was so minor that I never saw any puddles, the smell was all I could detect. I would suggest you do everything you can to pin point the leak before attempting to drop the tank, that can be quite a pain in the neck. Unfortunately it's in such a tight spot that it is difficult to inspect. Best place I've found to inspect it is to remove the spare tire and sit under the back with an inspection mirror and a flashlight. You can also use the mirror to work your way around the tank from beneath it. Hopefully you'll find your leak, before you invest any hard work or money.

If you do end up dropping the tank, I saw a thread on here the other day regarding tips and tricks for dropping/swapping it.

Good luck.