Operation of a Domestic Septic Tank
A septic tank can be supplied in many different forms, being manufactured from various materials such as square concrete blocks or bulbous fiberglass ones.
Installation consists of digging a large hole in the yard and inserting or building a tank in the excavation.
Clay fired or plastic pipe carries the greywater and sewage to the septic tank inlet, the pipe having a slight downward incline towards the tank. It is important to get this incline right; too much and the water will run away, leaving the solids in the line, too little an incline and the pipe will become clogged.
The water and sewage flow through the sewer pipe into the tank and the treated water discharges from the other side of the tank, both being about 3/4 way up the tank. An area is formed above and between the inlet and outlet pipes by two vertical segments that gathers the foam and scum, and several access manways are provided at the top of the tank for inspection and emptying the tank.
The sewage and greywater are subjected to natural bacteria treatment; the settle-able solids falling to the bottom of the tank forming a layer of sewage and solids sludge. The water and solids solution undergoes further bacteriological treatment, where oils and grease are removed and this forms a scum at the top of the tank.
The remaining treated middle layer of effluent exits the septic tank into a soakaway of small chips or stones. The soakaway can run the under the soil the length of the yard in a "herring-bone" shape to maximize the distribution of the wastewater.
Reference Web: lampreyseptic - septic tank maintenance.