We've just moved to an area with very hardwater, and I dont think the
previous occupants did anything to compbat limescale in the loo :-(
Despite
scrubbing and using a few of the off-the-shelf-from-teso limescale
removers,
the deposits havent budged.

I use two techniques. Depending on the deposit, either one or other of these
techniques should work. Open the windows and keep children away.

1. Pour in a good sized slug of brick acid. Scrub with toilet brush. Flush
several times.

2. Scoop out the water with a disposal plastic cup. Pour loads of standard
thick bleach all over the toilet bowl, allowing loads to drain into bowl.
Using old style Double Bleach Ajax scouring powder, sprinkle it liberally
over the thick bleach. Allow to soak for an hour. Scrub off. Flush.

Note that these techniques have considerable dangers from the materials
used. Alos, if you use the wrong bleach, you might produce chlorine gas,
which is poisonous.

Christian.