Our site services used concentrated sulphuric acid, plus some chemical to
enhance the action. Can't remember the name for sure (but "Blockbuster"
comes to mind) but it sure was dangerous as the burns on one of the team
demonstrated.
The safety instructions will be the standard ones for caustic soda / sodium
hydroxide. Bear in mind that even weak caustic soda is very dangerous to
skin and eyes (full face visor recommended) and will make soap out of you in
short order - and you may not feel anything until it's too late.

If it doesn't get round the u-bend, how do you expect it to work?
--
M Stewart
Milton Keynes, UK


Timothy Murphy wrote in message
...
My first-floor toilet is blocked, as far as I can see
just after the U-bend.

My local plumbers merchant gave me a jar of sodium hydroxide,
and told me this was as good as anything.
The label on the container warns me to follow the instructions carefully,
but unfortunately the instructions are missing.
Can I safely pour some down the toilet?
Do I have to ensure it will get round the U-bend?