The government has no official definition of "septic tank safe" in regards to cleaners but indicates any commercially available cleaner is safe for the tank when used in moderation and in accordance with the package directions, according to Consumer Reports. This includes disinfectants, bleach, toilet bowl cleaners and drain cleaners. The website indicates that "septic safe" labeling on containers is not meaningful.
Surfactants are the major ingredients in most cleaning products. These ingredients cling to the soil in the drain field and degrade into products normally found in nature, such as carbon dioxide, water and minerals. With a properly maintained tank, there are no surfactant residues in the surrounding ground water, indicating that the compounds have been completely removed before the wastewater returns to the water tables. Other ingredients, such as the fillers in dry laundry detergent, settle in the tank and become a part of the solid material removed during pumping of the tank.
Septic tanks generally hold up 500 to 1,000 gallons of wastewater. Their large volume provides a beneficial dilution factor when processing cleaners. According to the American Cleaning Institute, even if a user dumps an entire bottle of antimicrobial cleaner down the toilet, the system is able to provide effective disposal of the material. The same is true of disinfectants and bleach in a tank with proper installation and maintenance.