Need a low-cost way to salvage a vintage metal fuel tank with severe interior rust? Take the tank off the bike, and seal off the petcock hole. Pour in a couple of quarts of kerosene. Add a handful of nuts, bolts, and sheet-metal screws, and start shaking. The nuts and bolts knock the rust off from the inside, and the kerosene helps the rust flake loose. Keep shaking until your arms give out. Dump the nut, bolts, and rust out, refill with clean kerosene, rinse the bolts, dump them back in, and repeat over and over until the tank is clean. Rinse with solvent and coat the inside of the tank with a sealant.