I have a sewer drain pipe that's about 56 years old. Had to remove the plug to clean the backed up sewer line with an augger machine. The threads are gone and new plug won't attach. I even bought and installed a rubber test plug that expands when you compress it but it still leaks horribly any time water is in the line. Is there a tool I can rent or buy to re-thread a 4" hole?
No. Cast is cast. You can clean the threads with a tap, but you really can't tap new threads. Just apply a liberal coat of thread sealant to the thread area and your plug to get and stay dry. Otherwise, get a Plumber in to replace the clean-out fitting correctly. It's unheard of that the threads would ever wear or rust away, especially before the pipe, so it may have been a defective fitting from the start that was forced into use.
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