I've just cut out a damaged section of Cast Iron soil pipe to replace it with PVC. The pipe measures just under 4 1/4 in diameter, so I think it's nom. 4" pipe. I'm going to use Fernco rubber couplkings, but the size is a bit large for the Iron pipe -- should I sleeve it with something first? My mason mentioned that Green PVC Drain pipe will slide over this pipe -- have you heard of using this in this way?