is it okay to use the same black clamped banded coupling for cast-iron to PVC as it is used PVC to PVC ? the kind you see all over the place and can be found at any hardware store.
i just dug down to where there is a PVC hub mounted on cast iron and i want to replace the hub but the existing couplings have, on top of the rubber, an additional ribbed metal band (between the rubber and the clamp bands). as the metal band makes it look a little sturdier, i was wondering that the regular aforementioned type may not be strong enough.
What you're describing is known as a Fernco coupling (solid neoprene rubber) and a Mission or no-hub coupling (with a stainless steel sleeve). Fernco and Mission are just brand names of course.
Use the no-hub coupling for PVC to cast iron.