Drain the tank by putting a hose down the filler neck. Seal up the hose with a rag or whatever and put compressed air in next to it. The air will blow the fuel out the hose and into a bucket. Or siphon it the old fashioned way and get a mouthful of gas.

Are you replacing the tank? If so, just crank away with a long handled wrench and a persuader.

1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1956 Cadillac Sixty Special Fleetwood (The Godfather) | 1966 Oldsmobile Toronado (The Purple Knif) | 1966 Ford Mustang (Little Red) | 1964 Ford Galaxie 500 coupe | 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)