In alt.home.repair, on Thu, 27 Jul 2017 10:52:20 -0700, Oren
wrote:

On Wed, 26 Jul 2017 20:21:06 GMT, Wayne Boatwright
wrote:

ISTR, the blue stain is caused by acidic water in copper pipes.

Have you tried a cleansing power like Comet and a brush? Scrub it off
with the abrasive powder.


Those usually scratch the porcelain.

Be gentle once and awhile.

- flush

- sprinkle the stain area while wet

- slight scrub and flush.

Bon-Ami. Doesn't scratch.

I think there is a special product for copper stains but I don't
remember what it is, Zud?