Understanding Septic Tanks

Flush the Toilet

Want to see how a Septic Tank works?

This interactive septic system will help you understand how a septic tank works.  There are many elements to a smooth running system and all of these work together to create a wastewater disposal system that can work flawlessly when properly serviced and maintained.
Just flush the tank and see what happens!

  • Tank

    Everything that goes down any of the drains in the house (toilets, showers, sinks, laundry machines) travels first to the septic tank.  The septic tank is a large-volume, watertight tank that provides initial treatment of the household wastewater by intercepting solids and settleable organic matter before disposal of the wastewater (effluent) to the drain field.

  • Intake Baffle

    The intake baffle dissipates the energy of the incoming flow and deflects in downward.  The vertical leg of the tee extends below the liquid surface well into the clear space below the scum layer.  The upper leg should extend well above the liquid surface in order to prevent floating scum from backing up into, and possibly plugging, the baffle.

  • Sludge

    The “sinkable” solids (soil, grit, bones, unconsumed food particles) settle to the bottom of the tank and form a sludge layer.  The sludge is denser than water and fluid in nature, so it forms a flat layer along the tank bottom.  Underwater anaerobic bacteria consume organic materials in the sludge, giving off gases in the process and then, as they die off, become part of the sludge.

  • Effluent

    Effluent is the clarified wastewater left over after the scum has floated to the top and the sludge has settled to the bottom.  It is the clarified liquid between scum and sludge.  It flows through the septic tank outlet into the drainfield.

  • Scum

    Substances lighter than water (oil, grease, fats) float to the top, where they form a scum layer.  This scum layer floats on top of the water surface in the tank.  Aerobic bacteria work at digesting floating solids.

  • Outlet Baffle

    The outlet baffle is designed to retain the scum layer within the tank.  A sanitary tee can be used with the lower leg extending below the scum layer.  The elevation of the outlet port should be 2 to 3 inches below the elevation of the inlet port.  This prevents backwater and stranding of solids in the main inlet pipe during momentary rises in the tank liquid level caused by surges of incoming wastewater.

  • Distribution Box

    A distribution box is a concrete or plastic structure that has a number of openings.  Septic pipes fit into these openings.  This box helps distribute the effluent evenly to the drain field.

  • Drain Field

    The general and more technical term for handling the wastewater from the tank is the soil absorption system.  The most common type is the drain field.  Once sewage undergoes primary treatment in the septic tank, the clarified effluent flows to the drain field, where it is discharged into the soil for final treatment and disposal. 

    A typical drain field consists of several relatively narrow and shallow gravel-filled trenches with a perforated pipe near the top of the gravel to distribute the wastewater throughout the trench.  We always install Chamber System drain fields.  These are installed in a shallow drain field and replace the typical gravel and pipe system.  It consists of interlocked high-density polyethylene chambers that rest on the bottom of a shallow trench.  The chambers have louvered sidewalls and are open at the bottom, allowing the effluent to pass directly into the soil.

  1. Starting at your house, a main waste line leads sewage to your septic tank through the intake baffle. Beneficial Bacteria in your septic tank breaks down the sewage into sludge, effluent, and scum.

  2. When additional sewage enters the tank, the effluent overflows through the outlet baffle, through the distribution box, and is distributed into the soil absorption system.