I clean mine with glass marbles and a good solvent. Then use the 3M sealant if it is still to nasty for you. Cleaning can be a no win proposition as some have posted. But if you are dealing with an old truck like the 49 F!@# I last did the tank was $600.00 and it was way cheaper to clean than replace. There are companys that restore tanks, they cut them open and blast them, fix pin holes and reweld them back together then they coat them with the 3M stuff.

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"