I have cast iron sewer pipes. Several years ago, when the pipe was clogged, the plumber tried to remove the cleanout plug just inside the cellar wall. About a 3-inch piece of the threads that the plug screws into broke off at the bottom part of the opening. He replaced the cleanout plug with some kind of plug with a metal plate on the outside and a wing nut that expands the rubber (or whatever soft material seals leakage). Now, it's leaking and I fear that Im facing a huge repair bill, unless there is something I can do on my own. Please advise.