Berryman Chem-Dip is not a good fit for that application. However, Berryman B-12 Chemtool Fuel Treatment part #0116 or part #0101 can be used to remove sludge and varnish buildup from the gas tank. If the gas tank is small and can be removed, you’ll want to do so, pour the Fuel Treatment in, and either let it soak or better yet swirl it around before draining it. Repeat until the B-12 comes out clear and colorless.