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What Is A Septic Tank?

What Is A Septic Tank?

Houses and buildings in urban areas have sewers that carry waste to a treatment facility. However, those in rural areas, have a septic tank system in the yard. Septic systems consist of two parts: the septic tank, which is a concrete box buried in the yard, and the drainfield (see below for more information).

How does a septic system work?

  • Water flows into the tank through the inlet baffle (see diagram). This includes water from the shower, bath tub, sinks, toilet and laundry.

  • An equal amount of water then flows into the drainfield through the outlet baffle.

  • 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.

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


Example: 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.

What is A Drainfield?

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 (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 from the septic tank seeps 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 the home or building.

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.

  • Drainfields 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.

What Is A Drainfield?

Examples 0f Failing Drain Field

Click On Images For Detailed Explanation

Failed Drainfield

Failed Drainfield

This is another example of what can happen when your drainfield fails. This is raw sewage from your septic tank

Ground Above Drainfield

Ground Above Drainfield

This is what happens on the surface of the ground when the drainfield is failing. Wastewater from the septic tank cannot filter down through the soil because the drainfield is full of sludge. This sewage then puddles on the surface



This is an image of a drainfield lateral that is clogged with sludge. This septic tank has not been properly maintained.



This septic tank is above normal operating levels. The top of the liquid in a normal, well-functioning septic system should be between 6-10 inches from the top of the tank. It is only a couple of inches in this example.

Tree Roots

Tree Roots

This septic tank is infested with tree roots. They are so prominent here that it is impossible to see the sewage inside the septic tank. Tree roots love septic systems and are a major hindrance to the normal operation of a septic system. Tree roots infiltrate the pipes and cause blockages to the inlet line, outlet line, and drainfield laterals. They can even grow into the septic tank.

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