How septic tanks work

Septic tank systems are designed to treat wastewater that is generated in households. Generally, all water from sink,s baths, showers, washing machines and toilets all drain into a single pipe that leads to the septic tank which is buried outside.

When the wastewater enters the septic tank, the tank captures any solids in the waste and allows the wastewater to pass through.  The septic tank separates the wastewaterinto three different layers. Heavy solids sink to the bottom and form what is known as sludge. In the middle there is a clear liquid layer called wastewater. At the top of the tank, fats, oils and proteins accumulate to form a scum layer, see figure 1 below.

Once the solids have separated from the wastewater, and settled as solids on the bottom of the tank or into a scum layer at the top, the wastewater passes through the tank, and enters a drain field via distribution pipes. Distribution pipes have holes in them which allow the water to pass through them and be released below ground level into the soil (figure 1).

You can often see where the distribution/drainage lines are located in drier months as there is a green healthy part in your lawn, or your lawn grows a little higher. This is due to there being an adequate supply of water and nutrients from the septic tank.

Figure 1: How most septic tanks work: