Vinegar and baking soda to clean your sinks drains is very safe for septic systems.
In fact baking soda and vinegar can help prevent backups and keep your septic tank from smelling.
You can also pour 1 cup of baking soda down any toilet or drain once a week to maintain a good pH level in your septic tank of 6.8 to 7.6.
This can keep your septic tank working correctly and avoid septic problems.