Following years of sitting around, the 59 Corvette had serious debri and sludge accumulation inside the gas tank. Last season that I drove it (2010) I had to change an in-line fuel filter numerous times, so I finally pulled the tank out to see what I could do.
The tank resides behind the seats and is below the convertible top storage well. It comes out the top after removing a fiberglass cover. Realizing that it was indeed solid, I decided to take it to Redistrip of Indiana rather that buying a replacement unit. They had if for just a few days and were able to chemically clean the inside. they did an excellent job. It was complicated by the fact that this tank had a series of anti-slosh baffles in it to control the contents while cornering. Interestingly, Chevrolet did not use these in 59, but became standard in the 1961 Corvette tanks, so it seems someone before 1974 had replaced this tank with one of the upgraded versions.