By Don from West Bend, WI
Get down and dirty with Barkeepers cleanser and elbow grease. If that doesn't do it nothing will.
Usually the metal marks are "written" onto the porcelain like chalk on a blackboard.
Watkins Toilet Bowl cleaner or hydrochloric acid cleans that off quickly. Make sure the porcelain is completely dry first. Even the tiniest bit of moisture dilutes the hydrochloric acid to impotence, since they are not allowed to ship the pure stuff any more.
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Toilet Scratched By a Plumber's Snake. We recently had to "snake" the bathroom toilet, leaving scratch marks.