I used a H2SO4 commercial drain cleaner in my bath. The fumes from the cleaner reacted with residue of detergent on the surfaces of the bathtub to stain the surface to a rust color.
Any solutions to clean the stain on this porcelain bathtub?

Robemit

This is exactly why I don't recommend putting harsh chemicals in your drainage system. The only way I know how to remove rust and other stains, (short of refinishing the tub) is to soak a bunch of folded paper towels in bleach, put them over the affected area and let them leach out the stain. Just leave them there and keep pouring bleach on them until the stain's gone. Good luck, Tom

I used a H2SO4 commercial drain cleaner in my bath. The fumes from the cleaner reacted with residue of detergent on the surfaces of the bathtub to stain the surface to a rust color.
Any solutions to clean the stain on this porcelain bathtub?

Robemit
You can try CLR cleaner pour it on the stain let it stand for about 30 minutes, if that doesn't help try bleach. But keep in mind you may have damaged your tubs surface with the hydrocloric acid. You may have to have it refinished or replaced.