In article ,
"Christian McArdle" writes:
You can buy it as brick acid, I believe, from DIY stores and
builders merchants.

I'm planning to get some brick acid and pour it into my toilet. What
concentration would you recommend?

Doesn't need to be strong -- the scale dissolves easily with no
effort, just give it time. I use around a spoonful of Furnox
descaller (DS-3? -- large tubs available from B&Q or plumbers
merchant) dissolved in a pint of warm water and then poured
into the u-trap and left for an hour or overnight. You could
add a few drops of washing up liquid too if it's really bad,
but that's not necessary unless it looks really bad. (Don't add any
other cleaners as you might end up releasing clouds of chlorine
gas.) After leaving to soak, one wipe with the toilet brush and
flush, and brilliantly cleen loo, much more effectively and for
far less cost than any of the proprietry loo cleaners.

I've already tried emptying the trap and leaving it 24 hours with 2 litres
neat bleach filling the U-bend. It made it much cleaner, but there's still
loads of scale and general nastiness.

Bleach doesn't really clean anything like this, it just makes
the dirt invisible (for a short length of time).

--
Andrew Gabriel