pan pipe

Been renovating the bathroom, and onto the toilet! I had this covered whilst doing everything else so hadn't given it much thought till now. I had wrongly assumed that there was an adaptor onto the main out pipe, however none of it seems to shift at all. From the wall to the lip all seems to be...

I have a flexible pan connector going from my toilet, into the wall. The toilet pipe (on the left side) is standard ≈ 90mm Diameter But the wall pipe (on the right side) is non-standard and old and ≈100mm Diameter For some reason the pan pipe degrades once a year (maybe i have hungry mice) or...