A typical septic tank has a volume of 750-1500 gallons; may be made of concrete, steel, or fiberglass and is approximately eight feet long, five feet deep and wide. Septic tanks are watertight chambers that promote the growth of anaerobic bacteria for the biological decomposition of sewage and the separation of grease and organic particles from the wastewater. They are sited for a minimum detention period of twenty-four hours and are constructed with a pair of baffles or sanitary tees to prevent the flow-through of floating solids, to minimize the raw sewage from leaving the tank and from disturbing the settled sludge and floating scum.

Septic tanks are made with two top openings: one for each chamber. They are located so as to permit access to the tank inlet and outlet chambers. If your septic tank is not equipped with two access risers or markers it is important that they be installed for easy future location of lids and the septic tank. This is best done during the construction phase or at the time you uncover your septic tank for routine maintenance.

Septic tanks are designed to handle all the normal, daily (24 hour) effluent flow that a household or commercial enterprise can produce. For this reason, design is based upon the maximum capacity of a single family home in terms of personal occupancy, and bedrooms, i.e. 2 bedroom (4 people); 3 bedroom (6 people); 4 bedroom (8 people), etc. A commercial establishment is rated on its generated peak effluent load as determined by waste-producing fixtures or an actual flow of the prototype establishment. In a home, the design allows for the inclusion of laundry and the (not recommended) garbage grinder wastes. Roof and footing drainage, garage drains, end water softener waste must not be drained into the septic system.

Although minimum capacities for septic tanks (750 gallons) have been established, larger units have many advantages. Longer detention times, (due to the larger capacity), permit better separation and less carry-over of scum and sludge and tend to prolong the life of the subsurface disposal leach lines, leach beds, or seepage pits. Larger tanks require less frequent cleaning, are slightly more expensive and allow for future expansion of the home (i.e. additional bedrooms or waste discharge fixtures). They provide a good, cost benefit return particularly if accomplished during the initial installation. If the septic tank is upsized, the corresponding size of the leachfield must also be increased. The total septic tank process then produces an effluent that can be leached into most soils without clogging.


How a Septic Tank Works
The Typical Septic Tank
Leaching Systems
Maintenance Suggestions
Things are backing up.  What next?
How to Locate your Septic Tank
What can go wrong?
Pumping your Septic Tank
Septic Tank and Cesspool Sizes

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