Is it better to have a mission coupling (between the old cast iron waste line and the new PVC waste line) in the crawlspace or outside of the crawlspace?
Inside seems like it might leak and you would never see it. Outside means you have to go through the wall with the new PVC and that requires sealing issues.
Any opinions out there?
If its installed properly its not going to leak. You can install it, plug the system, fill it and let it sit for a while if it will help you sleep at night. Do it inside if its easier.
I'd use a Fernco brand coupling which is pretty reliable. You might want to clean the old cast iron pipe (wire brush) where it accepts the Fernco to insure good contact and no leaks.