In the middle of a new project in an old house. I'm relocating a toilet and adding a bath/vanity. I've got a 4inch cast drain that I'm tapping into. I currently plan to cut the current drain with a snap cutter, right behind the existing female flange and tie in PVC with a Fernco. On the other hand, there is a female fitting currently that is at the proper level and in good condition on the existing cast pipe (The old toilet elbow can come out reasonably easily). Is there an adapter that will fit "inside" the old female end that I would run my new PVC into - or am I better off just snap cutting and going cut end of Cast iron to cut end of PVC?