i just redid mine last week, i drained it sanded it then used duplicolor bedliner on the outside, cost me like 10 bucks, you can use a flap disk on a grinder, just make sure you drain the tank then fill it with water, or yeah you know what will happen. the inside of my tank wasnt dirty at all, just shiny metal, but i have use red kote on lawnmower tanks with excellent results