What materials/chemicals can I flush down the drain?

Septic tanks use bacteria to break down waste, therefore anything that kills bacteria will cause you a problem if used in excess.  Try to limit the amount of bleach, other cleaning chemicals and anti-bacterial soaps that go down your drains.  Look for toilet paper that claims to be safe for septic systems. Do not flush condoms, tampons, diapers, or cigarette butts, as they will not break down in your tank.