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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.

cleaning a septic tank

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

How often do you empty a septic tank?

How often you empty a septic tank depends on your septic system maintenance. It also depends on what you put into your septic tank. If you add a lot of coffee grounds, bad things like sanitary pads etc then you will need to have the septic tank pumped or cleaned more frequently. A good septic tank cleanout of the tank septic and the drip distribution system (drain field) will extend the life of your septic system.

Is a septic tank good or bad?

A septic tank is neither good or bad. The benefits of a septic tank are that they can be low cost if used properly and you don't have to pay monthly sewer fees or connection fees to a municipal sewer.

Why do we need septic tanks?

Around 20% of the population of the United States are not connected to a county sewer and therefore need a way of wastewater treatment and ultimately discharging that greywater safely into the environment.

What are the disadvantages of a septic tank?

The main advantage of a septic tank is you do not have to pay monthly fees to the county to treat your sewage.

How did old septic tanks work?

Concrete or steel were used to construct an early American conventional septic system. By the 1940s, the conventional septic system was widespread throughout the United States, and by the 1960s, when these systems began to fail, significant improvements to the system as a whole were made. Most modern septic systems use more advanced materials, such as fiberglass, precast concrete, polyurethane, and other plastics. Older septic systems resulted in mainly anaerobic bacteria, but many of the systems put in today utilize an aerator which result in aerobic systems.

What should be the size of septic tank?

The size of a septic tank will depend on factors such as the number of bedrooms, soil condition, lot size, and more.

How is plumbing from house connected to septic tank?

The house is connected to septic systems via the main drain line.

Should you use a garbage disposal with a septic system?

You can use a garbage disposal with a septic tank but it is important to use this sparingly. Composting organic material in a compost pile rather than down your kitchen disposal is a much better idea. Excess use will lead to a build up in organic material and solids settle and can be hard for natural bacterial activity to break up.

What is the alternative to a septic system?

The only alternative to a septic system is a sewer if your property is connected.

What is the main septic tank design in the US?

Septic tank designs have progressed with modern septic tank systems. Today the certain septic tank designs are popular in the United States to treat wastewater. These are primarily two-chamber plastic, fibreglass or concrete septic system.

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