I have discovered yet-another-leak in an en suite installation only 3 years old! It is very slight - and appears to be coming from a saddled on 1-1/4" waste pipe boss going into the top of a hoizontal 4" stack extension. The cause of the problem is the boss being mounted too close to the outside wall through which the stack extension passes. Looks as though the boss was fitted to the 4" pipe, then the 4" pipe pushed through the wall to meet the tee in the vertical stack. Not enough distance between outer end of 4" pipe and boss, so boss is jammed against plaster surface and a leak results.
So that's the problem, how do I effect a repair. Thorough method would be to remove toilet and horizontal pipe through wall, fit new 4" pipe with correctly positioned boss, modify 1-1/4" waste piping to suit.
As this leak is so slight I would like to try a repair type sealant (I think I can just about get enough access round the boss having hacked the plaster from behind it).
So does anyone have recommendations on suitable sealer for this please?
TIA
Phil