Septic Tanks

Collection tank that allows solids to settle and be decomposed by anaerobic bacteria.

Treatment Level:  Primary
Relative Cost:
Amount of Maintenance Interaction:  low
Beneficial Byproduct:  little (compostable sludge)


  • Long accepted practice with many on-line O&M resources.
  • Very efficient at retaining solids, oils & greases.


  • Must be careful not to flush products that are harmful to the tank bacteria.
  • Unpleasant to clean if no pumping service is available.
  • Secondary treatment and sludge disposal options needed.

Operation & Maintenance

  • Inspect every 3 – 5 years to check for level of solids, odors or insects in vicinity of tank, and pump function
  • Remove accumulated solids when tank is 1/2 to 2/3 full, or nearing outlet pipes
  • Only add microbes to improve waste digestion if no on-site secondary treatment is provided.

Blackwater vs Graywater?

  • Can treat both in combination, but diverting the graywater will help make the tank & secondary treatment measure smaller

Secondary Treatment Options

Additional Notes:

  • Need to locate in an area with easy access for inspection & maintenance
  • Holding tank is typically concrete, fiberglass, or plastic & is water tight
  • Best to have multiple chambers for cleaner effluent
  • Typically pump to secondary practice
  • Watch what you flush!  Minimize bleaches & chlorine, don’t use caustic products or drain cleaners as these things can kill the beneficial bacteria in the tank