Tree roots once caused sewage to back up into our basement. I got tired of the temporary fix and had them dig up my lawn and install PVC pipe right from the foundation to the big new main under the street. It seems that the basement smells even MORE like sewage, despite pouring bleach down the two basement drains, and also into the old (idle) sink which I hope to revive soon. Who can help me!! I’m ready to sell the joint!
I would call a plumber to possibly ckeck your plumbing with a smoke bomb. Sewer districts will often use this method to check systems to find connections that are open, such cleanout plugs missing etc. this could locate broken pipes in walls.