On Tue, 9 Apr 2013 14:12:06 +0000 (UTC), HerHusband
wrote:

If you are on a septic system, I would try other alternatives before
dumping acids or other caustic chemicals down your toilet. You wouldn't
want to cause problems with your septic system just to remove a stain.

If muriatic acid ( what I use for calcium crud) is used on a septic
system, simply neutralize it with baking soda before the flush. It
will not harm the septic system. I'm on city sewer with PVC pipe.
If metal pipes, also use the baking soda before you flush.