Need to replace pipe running from tub to sewer line. Line is currently metal which is deteriorating and causing structural damage. Line is approximately 12 in straight into sewer. What is best method to remove damaged line and replace with pvc or metal. Thanks

The first thing I would do is remove the metal drain line and trap all the way back to the sanitary tee in the stack. Next I would go to to the tee and if it's threaded I would convert to PVC using a PVC male threaded adapter. You may now redo the drain and trap using PVC. Good luck, Tom