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If not properly maintained, an on-site septic system could cost you up to $20,000 to repair or replace. The following provides technical information and tips to help you avoid such an expense. 

Septic Tanks
All on-site septic systems have a septic tank, a large container that is buried underground and is made of concrete, fiberglass or polyethylene.  The septic tank protects the absorption ability of the subsoil by:

Removing solids from liquid.  As sewage enters the septic tank, heavy solids settle at the bottom and forms sludge, which reduces the flow of sewage into the tank.  While grease and other light solids rise to the surface (scum), both the sludge and scum are retained and break down while the liquid (effluent) is passed along to the drain field for absorption by the soil.

• Providing biological treatment. Bacterial activity breaks down the solids and liquids in anaerobic conditions (without oxygen), which are referred to as “septic,” the name given to the tank.
  

• Retaining scum and sludge.  Scum, the mat of floating solids and grease, and sludge, the solids that build up in the bottom of the tank, are eventually compacted into a fraction of its original volume.  Warm geographical regions of the country allow for a more complete breakdown of the scum and sludge than cool regions.  Hence, tanks in warm climates tend to not require pumping or cleaning out as frequently as tanks in cold climates.  Note that it is important to maintain a sufficient volume for solids to accumulate between pumpings and cleanings in order to avoid having the solids enter the drain field and clog the soil.

Septic tanks should provide at least 24-hour retention time or at least 750 gallons for a one or two-bedroom house; 900 gallons for a three-bedroom house; and 1,000 gallons for a four-bedroom house.  250 gallons should be added for each bedroom exceeding four.

Kitchen grease is generally detrimental to the septic tank’s operability.  Small amounts of kitchen grease can enter the septic tank without damaging the system.

 

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