For a number of YEARS my toilet leaked slightly every time it was flushed owing to the failure of the rubber seal where the pan joined the sewer pipe. Expert opinion said: "We'll cut this pipe, replace this section, install new plastic link with new seal, replace the pan, etc, etc." Didn't even ask how much. I then stuffed this stuff all around rubber seal, plus a couple of extra layers over he seal itself for good measure. Since then, not a drop. As far as I can tell it would stop Niagara. Horrible to work with, a fibrous gunge which dries grey/black, but it works and who is going to look around the back of a loo? Mind you, a proper translation of what it says on the tin would help. The instructions in several languages are helpful but should be more detailed.