TV Inspected the sewer line from the outside cleanout back to the vent stack. Found the 2-inch connections from the laundry, kitchen, and bath sink tying in at the base of the stack above the 90-degree elbow. The shower connects through a second 2-inch line. Recommended removing the vanity and toilet to open the bathroom floor and replace the 2-inch connections at the base of the stack. Plan to leave 2 feet of 4-inch PVC downstream and line the 4-inch cast iron from the outside cleanout to the new 4-inch PVC.