Your septic system is made to deal with human waste and toilet paper, as well as water from toilets, baths, and sinks. Everyday household cleaners, detergents and bleach will not hurt your system if used in moderation. Anything else that you are putting down the drain may cause your septic system function may be impaired. You should never pour oil, cooking grease, paint, or insecticides into your plumbing system. These items can hinder bacteria growth which is critical to the proper functioning of your system or they can plug the pores of your system and hinder the system to drain properly.
Non-degradable paper products, such as diapers, sanitary napkins or tampons, and paper towels are very harmful to your system. Also, do not put any other non-biodegradable substances such as plastic baggies or plastic wrap, or cigarette butts. These items can cause clogging problems. You should have your tank pumped more frequently if you have a garbage disposal but it will not hurt your system if it was designed for it.