The answer to 'septic tank foul smell' is that a foul odor coming from your septic tank is typically a sign of an issue that needs to be addressed. Common causes include a full septic tank, a blocked or damaged septic system, or a problem with the septic field. Symptoms may include a strong rotten egg smell, sewage backup, or slow draining plumbing.
In many cases, the solution is to have your septic tank pumped and inspected by a professional plumber. They can diagnose the root cause and recommend the appropriate repairs. However, some minor issues like a blocked vent pipe may be something you can fix yourself. But it's best to call in an expert if the problem persists or you're unsure of the cause.