The answer to 'why is my septic tank foul smell' is that a foul odor from your septic tank is usually caused by a buildup of gases or a problem with the tank's functioning. Common causes include a full or clogged septic tank, a broken baffle, or a problem with the drain field. Symptoms may include a strong rotten egg smell, gurgling noises, or sewage backing up into your home.
If you notice a foul septic tank odor, it's important to address the issue promptly to prevent further problems. You may be able to resolve minor issues like a blocked vent pipe yourself, but more serious problems like a full or damaged septic tank will likely require the help of a professional septic system service technician.