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How does my Septic Tank work?

 Clean Septic Tank

All conventional septic systems have a septic tank, which is usually a large buried rectangular or cylindrical container made of concrete, fiberglass or polyethylene. Wastewater from all plumbing fixtures drain into the septic tank. Heavy solids settle to the bottom where bacterial action produces digested sludge and gases. Lighter solids that float such as grease, oils and fats, rise to the top and form a scum layer. Systems constructed before 1975 usually have single compartment tanks. Those built from 1975 and on are usually two compartment tanks. This is important to know when having the septic tank serviced, as both compartments of a two-compartment tank need to be pumped.

Cross-section of a two compartment septic tank

Two Compartment Septic Tank

Cross-section of a single compartment septic tank

Single Compartment Septic Tank

Over time, the sludge and scum layer will build up in the tank until the baffles are blocked. This forces waste into your drain-field, resulting in premature failure, or it will cause a backup in the house. Pumping is necessary to give it a fresh start. The tank does not have to be full of sludge for this to happen. The baffles, especially the center one, hang down halfway to the bottom. Once the sludge has built up to this point, the flow is blocked & a backup will occur.

Domestic Septic Tank
Septic Pumping Near Deer Park Wa

Bacteria must be present in the tank for the organic material to break down. Harsh chemicals soaps and antibiotics kill bacteria. If to much bleach, dish detergent, antibacterial soap, acids etc, are flushed into the tank the scum layer stops decaying & builds up until the baffles are blocked & the tank backs up. Enzymes can be used to accelerate the decay process. However, it does not remove the waste from the tank or eliminate the need for routine pumping. 

How often should I pump my septic tank?

 Septic Pumping Pump Chart

We do not recommend waiting until your tank backs up to have it pumped!  The force of the water entering the tank pushes the sludge into the second chamber. When it fills, it's forced into the drain field. Repairing a drain field costs thousands of dollars & is never worth the risk. Routine tank pumping ensures your system will work properly for many years. 

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