The main sewer out of the house is 3" cast iron, built around 1960. The clean out is a cast iron tee with a brass plug, about 2 feet from the foundation. The plug has come loose and the CI treads are rusted and swelled so that I can't screw in a new plug. Grade level has increased about 10 inches over the years, so I want to put an extension to grade as well. What is the recommended repair. (I am capable of DIY) Is there some kind of doughnut or other reducer, or should I cut out the tee and replace it with PVC and rubber connectors? If I have to replace the tee should I use a Y or tee?