I wanted to replace an old P-trap toilet pan (sewer pipe comes from the wall not the floor) with a new one. The new pan sits closer to the wall than the old one by 110mm, therefore the sewer pipe that comes from the wall (i.e. 100mm diam. Steel pipe) need to be cut. I plan to cut this using a grinder, then join the sewer pipe from the wall with the one from a new pan (100mm ceramic pipe) using sewer pipe collars. Some collars have black rubber surrounds it to seal gaps. I am not sure if I should use the one with rubber or without. The one with rubber has an inner pipe dimension of 90mm. Is this the right size?
Thanks for your help.