Small amounts of household bleach used as directed for normal cleaning are generally compatible with a septic system. Concentration and quantity matter: pouring leftover bleach or large amounts of disinfectant down a drain is different from using a diluted product for its intended task. Follow the product label and any instructions for your particular treatment equipment, and avoid using more cleaner than the job requires.
Do not mix bleach with other cleaners, and avoid automatic toilet dispensers that add bleach with every flush. Take unwanted concentrated chemicals to an appropriate household hazardous-waste collection service instead of emptying them into a sink. Keep the equipment manual with your service records so its care instructions are easy to check. For help organising routine system care, see our maintenance and operation plans.