What is the best way to clean a stain off concrete. Outside of my home garage we were parking the electric golf cart. It sat for a month or two and when moved it left a reddish brown stain on the concrete. I have a 4000psi pressure washer and have tried simple green, laundry detergent, grease lightning, and elbow grease with a heavy brush. These solutions didn't work. I do have some On and Off a boat hull cleaning product that has a burning effect if you get it on your skin. Should I try this?