Thanks for you input fellas.

I ended up buying something called "The Works" at Walmart. It is a toilet bowl cleaner.

Put it on and wipe it off and the brown is gone just like that. But holy crap. Be careful. Cover any open wounds or cuts, cause this crap is gonna burn.

And another thing. Use in a well ventilated area. This crap will almost knock you out.

Oh, and wear old clothes. Got a couple drops of it on my clothing and within 5 minutes it had eaten a hole in them.

Think it cost about 1.50 per bottle and I probably only used 1/10th of a bottle. Cheap and potent.