I have a clearance problem running a waste pipe between where I want
to put a washing machine and the adjacent wall. I need an extra
couple of cm compared with the existing 40mm waste pipe that's there.

Can one get rectangular waste pipe with adapters to and from 40mm? It
would be a perfect solution for me. It's not a waste pipe that needs
a lot of capacity, it just runs from a cloakroom wash basin.

I can't really chase the pipe into the wall as access is very
difficult.

--
Chris Green