Septic Tank Cross Sections
2 compartment Septic Tank - (1980 to 2008/2009) 1 compartment Septic Tank - (up to approx 1979)
 
Septic Tank Functions
- Settling and Flotation
- Anaerobic Digestion
How a Septic Tank Functions
- Provides primary treatment in an on-site wastewater system.
- Wastes enter the first chamber of the tank.
- Heavy solids settle to the bottom of the tank and form a sludge
layer.
- Light wastes (grease, hair) float to the top and form a scum
layer.
- In a two compartment SepticTankall steps are repeated a second time; this almost invariably provides proper treatment
Things that Degrade a Tank Slowly
- Garbage Disposal Refuse
- Hair
- Laundry Lint
- Powdered Laundry Detergent
Frequency of Pumping
- General Recommendation, every 3-5 years.
- Frequency of pumping is best evaluated at time of service.
What does NOT belong in the tank?
- Cigarette Butts
- Coffee Grounds
- Cooking Fats
- Paints and Chemicals
- Paper Towels
- Sanitary Napkins, Tampons & Applicators
- Disposable Diapers
- Condoms
Septic Tank Materials
- Reinforced Concrete (most new tanks in King county & Pierce County Washington)
- Fiberglass
- Polyethylene
- Older Tanks: Steel, Concrete Block, etc. (Prior to the 60's)
Tank Sizing
- Generally prescribed by the Health Department for individual
homes. Only 1500 Gallon tank are installed in King county as of 2009
- 1000 Gallon Tanks where installed in King County up until 2008 - 2009
- 750 to 950 Gallon Tanks were installed up to appoximately 1979
 
Risers
- Provide easy access for service or emergencies
- A must for effluent filters (filters should be cleaned yearly)
- Shallow tanks - short risers
- Joints must be water tight
- Grade away from riser (prevent infiltration)
- Covers must be secure (prevent infiltration & gases from escaping)
Effluent Filters - Function
- Reduce suspended solids
- Protect against not pumping
Myths and Wives Tales (false information)
- "A good working septic tank never needs Pumping/Cleaning."
- "Septic tank additives will maintain your septic tank or system."
(At certain times, additives may be helpful. This is best determined at
time of cleaning)
The progression of the Septic System
Give us a call
(425) 432-3084 (253) 639-3606 (360) 825-4809
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