The answer to 'why is my sewer line constantly running' is that there could be several common causes, including a clogged or damaged sewer line, a problem with the septic system, or a plumbing fixture that is continuously running. Symptoms may include slow draining sinks or toilets, gurgling sounds, and sewage backup.
Some potential solutions include using a plunger or drain snake to clear a clog, repairing any cracks or breaks in the sewer line, or addressing issues with the septic system. However, for more serious or persistent problems, it's best to call a professional plumber who can properly diagnose and fix the issue.