Disposal of non-biodegradeable objects (such as flushed items, hair, etc) can get lodged in the pipes and cause a back up. Additionally, use of solvents and chemicals down your drains, can reduce the natural decomposition of the solid wastes in the tank, causeing the level of sludge to rise and back up the system. Not pumping out your system on a regular basis (once every 2-3 years) can cause back ups. Excessive disposal of oils and grease may cause your drains to block and are not digested easily in the septic tank. Additionally, some cleaners and chemicals (bleaches, solvents, etc) can damage the working of your septic tank and should be properly disposed of. Garbage disposals can be used with septic systems, but should be used with restraint to prevent unnecessary strain on the septic system.