What Is A Septic Tank?

Most people are unaware of how their septic tank system works. People living in urban areas have sewers to carry the waste to a treatment facility. Those who live in rural areas, however, have a septic tank system in their yards.

Septic tank systems consist of two parts, the septic tank and the drainfield.

  • Many different things happen when water and waste enter the septic tank.


  • Inorganic solid material, which is generally more dense than water, sinks to the bottom of the septic tank and forms the "sludge layer".


  • Organic material, which is generally less dense than water, floats on the surface of the water. This is referred to as "the crust" or "the scum" and it can consist of hair, toilet paper, solid waste, grease, etc.


  • The water from flushing the toilet, using the sink, doing laundry, etc. flows into the tank and an equal amount of waste water then flows into the drainfield.


  •  Bacteria naturally found in our digestive systems begin breaking down the organic material in the septic tank and converting it to liquid form.



A normal, well-maintained septic system performs as follows:Someone takes a shower, using approximately 40 gallons of water, and the water, soap, and dirt flows into the septic tank from the inlet line. The dirt sinks to the bottom in the sludge while some of the soap and grease floats on top of the water. Approximately 40 gallons of water slowly flows out to the drainfield through the outlet line over the next several hours.

The drainfield (or Leeching System) lies beyond the septic tank and is the area where waste water is incorporated into the underlying ground. The soil acts as a natural filter and cleans the water as it sifts through the soil.

An outlet pipe (plastic pipe going from the septic tank to the drainfield) will lead to a header pipe. This header pipe has several perforated pipes extending off of it and these are encased in gravel. The drainfield will become clogged and cease working correctly if sludge/scum/crust from the septic tank seep through the outlet pipe and into the drain field. This will prevent water from filtering into the ground, causing septic waste to back up inside your home.

How do the sludge and crust/scum clog the outlet line?

(refer to the diagram of a septic tank on the upper right)

The sludge and scum levels are constantly increasing. Sludge/scum are added to the septic tank every time someone does laundry, washes the dishes, flushes the toilet, etc. This shrinks the amount of available space for waste water. The septic tank is now less effective as there is now less space and time (less space means water is retained for shorter periods of time and funneled out into the drainfield faster) available for the waste and dirt to separate from the water.

Without proper septic tank maintenance, this results in the sludge/scum passing out into the drainfield. THIS IS NOT GOOD!!! The drainfield now becomes clogged and unusable from the sludge/scum and will need to be replaced.


Two things to remember:

  • All drainfields are not created equally. Each has a limited capacity which is affected by a number of things including but not limited to: elevated levels of groundwater, size of the drainfield, type of soil, number of people living in the house, age of drainfield, tree roots, etc.


  • Every drainfield will fail eventually and they cost thousands of dollars to replace. BUT you can extend the life of your septic system by minimizing the amount of solid waste that enters the drainfield. This is primarily done through regular septic tank maintenance.


Click On Images For Detailed Explanation


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