I have a house built in the 1970's. The sewer system seems to have two seperate side. One side works fine but, the other has issues. I have an issue with water backing up or flowing slowly from a basement toilet which the sewer line is in concrete. For a while everytime the washing machine would discharge the toilet would gurgle and get black material in the water and water would back up into the shower which is only 5'-6' away. My brother-in-law, who is a plumber, and I took off the toilet and there was black sludge there which we took out and ran a power auger through the drain and we ran hot water through the drain. Seemed to be clear. A few day later we noticed that when we ran water in out kitchen sink up stairs water would leak around the base of the toilet in the basement and when we flush the toilet water leaks badly so we haven't used. The washing machine no longer causes problems. My brother-in-law is stumped and thinks we need to run a camera in the line. I am stumped. Any ideas without breaking up concrete floor?