I have a house in town which was built in 1975. In 1986 the plastic waterline got brittle and I had to replace it. The waterline was near the sewer line. I remember some 29 years ago that the PVC plastic sewer line got cracked on top by the backhoe bucket. It didn't cut a hole, just a crack or split. The backhoe guy I had hired saddled a half piece of PVC plastic the same size as the sewer line over it and said it would never be a problem. Now the sewer line is easily in the weep line of a 33 year old soft maple tree. I am pretty positive roots have gotten in. It seems like I have had some success keeping it operating with some "main line sewer cleaners", but the problem always comes back eventually. Might be a month or might be six months. I can dig it up, but was just wondering if there was an easier remedy that might work. How does salt work??? Copper sulfate??? Had a plumber run the "power sewer cutter" down it in January. Problem is back. Thanks for your ideas.