Grind it off with that, then an acid etching, then primer then the paint.  

The metal you own will always weigh the same amount (if you take care to keep it out of fires, acid or the like).

I snaked it, replaced the S-trap and poured acid down the drain to get everything else clear in the pipes.

I looked how to solve this problem in this guide Best result were after using spray with boric acid.

Muractic acid!!! 

He used everything up to muriatic acid, and the smell remained... 

You have to use much more concentrated acetic acid to get the job done and of course the yard will stink of vinegar, but it makes the average organic fanatic happy at a slightly elevated cost for faster equipment degradation.

This corrosion happens when formic acid accumulates on the coil as a result of the interaction of water, copper and volatile organic compounds (VOCs) in your indoor air."

BORIC ACID.

One guy I know putts muriatic acid into the clean outs to unstop the leach filled lines.