The answer to 'my sewer line smells bad' is that a foul odor coming from your sewer line is usually a sign of a blockage or problem in the plumbing system. Common causes include a clogged pipe, broken or cracked sewer line, or buildup of organic matter and debris.
Some common symptoms of a smelly sewer line include a rotten egg or sewage-like smell, slow draining sinks or tubs, and water backing up in your home. Solutions can range from using a plunger or drain snake to clear a clog, to repairing or replacing the sewer line. If the problem persists or you're unsure of the cause, it's best to call in a professional plumber to diagnose and fix the issue.