What Is A Septic Tank? Everything You Need To Know About How Septic Tanks Work

If you live in a house without access to public sewage, you'll likely rely on a septic system to get rid of human waste and wastewater or liquid waste. According to the Environmental Protection Agency (EPA), more than one in five households in the United States depend on a conventional septic tank, individual onsite or small community cluster septic systems to treat their household human waste and liquid wastewater.

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What is a septic tank?

A septic tank is a large concrete, plastic or fibreglass reservoir or compartment with a typical capacity of between 1,000 and 2,000 gallons. A septic tank is installed underground, typically 50-60 yards from the house depending on local regulations and is watertight. Septic tanks are connected to the household plumbing via an inlet wastewater pipe, and the other end is connected to a septic drain field (also known as a leach field, absorption bed or absorption field. Usually, the inlet pipe and outlet pipe connections are made with a T pipe, which enables the solid and liquid waste (untreated waste) to enter and the treated wastewater to exit. The T shaped outlet prevent the solid waste, organic matter or accumulated sludge to exit through the outlet pipe and into the leach field, avoiding costly clogs. Internal chambers are commonly found in modern septic tanks, each having an access opening and cover, and separated by a dividing wall with openings located approximately midway between the floor and roof.

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How does a septic tank work?

A common question is how does a septic tank work or septic system work. Septic tanks are large, watertight containers designed for wastewater treatment for greywater and solid waste to settle and undergo a separation process while anaerobic bacteria work away at the waste particles. Solid waste settles to the bottom of the septic tank, separating from the wastewater and scum or grease. Bacteria eat away at the sludge and break it down into simpler components over time. This process separates out scum, such as fats, greases, and oil which floats to the top of the water layer. This process creates three distinct layers in the first compartment; scum on top, wastewater in the middle and organic sludge or solids on the bottom of the septic tank. The liquid layer moves through the septic tank's dividing wall and into the second chamber, where further settling takes place.

After the solids are filtered, the filtered liquid wastewater is now in a relatively clear condition in the pump chamber. From the second chamber, the treated effluent exits into perforated pipes or a drip distribution system known as the leach field also referred to as a drain field, drainfield, seepage field.

The effluent slowly releases into the drainage field and, over time, soil and gravel filter it. This is the final waste water treatment for the septic tank effluent, using the soil to slowly remove impurities.

Septic system processes step-by-step

  1. Water waste the household plumbing produced from your kitchen drains, bathroom, shower and laundry plus effluent from the toilet makes via the main drainage pipe and through the inlet pipe into the big underground tank.

  2. Beneath the ground, the septic tank starts the process of treating the waste water. It must keep this long enough for the solids to settle to the bottom, while oil and grease rise to the top.

  3. In modern septic tanks, an effluent filter is attached to the outlet pipe to stop any organic material or solid particles to enter the drainage field. In older septic systems an effluent filter can be added by a septic contractors.

  4. The liquid wastewater (effluent) will then be able to drain out of the tank into the drain field as a consequence of this process.

  5. This wastewater exits septic tank systems through perforated pipes where the wastewater percolates onto porous surfaces of sand, gravel or shallow soil below the ground surface, which act as a filter.

  6. The shallow soil acts as one further treatment accepting and filtering as it disperses wastewater through the soil, eventually discharging to groundwater.

  7. Finally, as the wastewater dissipates into the soil this naturally removes harmful coliform bacteria and other viruses found in human waste. 

Frequently asked questions

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