Until you return flushed with success?Thanks for helpful replies.
The rest of the usual suspects can bog off...
I once used spirits of salts to clean paint off a marble fireplace when you could buy it in a glass bottle from ordinary hardware shops.Janitorial supplies sell a toilet cleaner that contains hydrochloric, cleans it in seconds.
Edit: They also sell a mop thing to use with it, or at least they did when i last used the stuff.
This is the best thread ever created on C.C