Limescale is building up round the inside of our toilet bowls (not under the water). We live in a hard water area. I use orange Cillit Bang everywhere else (shower/taps etc) but it sort of slides off the toilet bowl rather than staying there and doing it's job! What can I put on it that's really thick so will stay there and melt it for 10 minutes before I give it a scrub (or ideally put it overnight and not have to scrub it at all??)