The answer to 'sewer line foul smell' is a sewer line problem that needs to be addressed promptly. Common causes include a blockage, crack, or break in the sewer line, which can allow sewage gases to escape and create a foul odor. Symptoms may include the smell coming from drains, toilets, or outside the home, as well as slow draining or gurgling noises.
The solution often depends on the underlying cause. Minor clogs may be cleared with a plunger or drain snake, but more serious issues like a damaged sewer line will require professional plumbing services. It's best to call a licensed plumber to diagnose and repair the problem, as attempting DIY sewer line repairs can be dangerous and may make the problem worse.