Yes, you can put root killer directly in the septic tank, but it is essential to do so cautiously. Use root killers specifically designed for septic systems and follow the manufacturer's instructions carefully. While root killers can help eliminate intrusive roots, excessive use can harm the septic tank's beneficial bacteria, leading to system issues. It's best to consult a professional before using root killers in your septic tank to ensure it's done safely and effectively, minimizing any potential damage to the system. Regular maintenance and proper root killer application can help keep your septic system running smoothly.