On Mon, 29 Apr 2013 13:16:03 +0200 ehernandez wrote:

I guess its okay to use it as long as you follow instructions. I usually
just pour a little in the toilet bowl and cover it for 30 minutes

The main problem with pouring into the toilet bowl is that much
of the staining is up near the top of the bowl and that much of
the scale is inside in the channels that the water follows.

After having done it the correct way, and having also done it
the incorrect way, I can definitely suggest what I found to be
the best method.

BTW, gloves are helpful; a mask isn't really needed; and eye
protection is a good idea in case you accidentally splash.

0. Don't be stingy on the acid (a gallon is a good amount).
1. Empty the toilet bowl of water (any way you want).
2. Plastic wrap the bowl (no need for tape).
3. Ventilate (a fan is enough but windows are good too).
4. Pour acid slowly using a funnel (no splashes!).
5. Plastic wrap the tube (no need for baggies & rubber bands).
6. Wait an hour (this is the slow and easy method).
7. Remove plastic & pour baking soda (it will use a lot!).
8. Remove tube plastic wrap over tank tube (ask me why).
9. Flush like there's no tomorrow (10 flushes is good).
10. Inspect & reapply as needed.

Note: If you cup and re-use the acid, you can get away with
a quarter of a gallon; but it's not worth saving the half
hour or the gallon to expose yourself to more HCl fumes
than you need to be exposed to (but don't expect to be
fume free. If you can't talk for a few minutes, then you
got way too much; but otherwise, expect a few whiffs of the
stuff to the point that you immediately notice it, and you
simply hold your breath and move away to breathe again
until the ventilation system removes those fumes.