The answer to 'sewer line constantly running' is that a constantly running sewer line is typically caused by a clog or blockage in the sewer line. This can be due to a buildup of debris, tree roots, or other obstructions in the pipe. Symptoms may include slow draining sinks, gurgling sounds, and sewage backing up into the home.
In many cases, the solution is to have a professional plumber use a sewer snake or hydro-jetting equipment to clear the blockage. This is not a job that is typically recommended for DIY, as improper techniques can damage the sewer line. It's best to call a licensed plumber to diagnose and address the issue properly.