right-tricky (maybe) but need some help here!! i have a boss shoulder - (110mm) for a soil stack, it has 3 spaces. I know i need to drill a hole in the spaces required, using a hole saw - but, do I just insert a rubber push fit boss adaptor and then put my waste pipe (40mm) into that - or does the boss adaptor have to be solvent welded to the boss on the shoulder first?!! i am a bit confused but i don't want any leaks!!! any helpor advice will be so appreciated.