Outside diameter
If your talking about baking soda and vinegar -- NO --
stop trying to cheat on fastenal FSB courses.
PVC is a compound.The pipes are not a compound but they are made from a compound.
Pvc pipes are cheaper. They are easier to join. They last longer.
PVC stands for polyvinyl chloride, which is what PVC pipes are made of.
Because modern PVC and PEX pipes are much more efficient and easier to work with.
4inch or 100mm PVC sewer lines are the best way to go. as amater af fact if you are in Australia they are the legal way to go. 3" or 75mm is only used for stormwater pipes from the gutters.
These days PVC pipes are faster and easier to fit and in many ways more efficient than cast iron.
PVC pipes are less expensive and easier to repair. Metal pipes are more expensive and more difficult to repair.
pVc pipes? Hacksaw
I can't imagine the plumber only giving 1 year on the PVC. Cast iron is rough on the inside and those rought spots can snag paper, lint, etc, eventually leading to blockage. PVC should last much longer and be less susceptible to blockages from material getting caught on the inside wall of the pipes. Also, PVC doesn't rust, while cast iron will. All-in-all, I'd have to vote for the PVC (make sure that it is at least Schedule 40 PVC).