I use Sno Bol, a hydrochloric acid solution. I cuts right
through the schmutz, something chlorine+determent
products cannot do.

When I say "schmutz", I mean hardened fecal schmutz.


A while back Harpic released an acid based bog cleaner
that they claim to be best on the market for shifting limescale,
I've found if the limescale is stained at all it takes an awful lot
of bog cleaner to shift it -- whiten the limescale with bleach first.

There's an American product called CLR (calcium-lime-rust) specifically for
such stuff.