I need advice for the below picture. The waste line plugged up and the clog couldn't be cleared. So I am now gutting the bathroom. (The house is from 1915 but we were told it was remodeled in 1948.) The sink and toilet lines are galvanized and the main line is cast iron. Above the "T" in the vent line for the sink, plain 2" steel was used. It completely rotted away and filled the line with debris. My question is can I snap the cast iron at the elbow where it comes out of the wall and transition to PVC with a Fernco? The main line was scoped and it was in good shape. If I snap the cast iron i wont have to destroy the old plaster walls to try and repair the toilet and sink lines. Thanks in advance for the help.