The septic tank and septic system are amazing working parts of your home that you rarely think about it or see. There are several different types of septic tanks and systems used today, however we will discuss the most common one, a conventional system.
All water goes into the septic tank
When you wash your clothes, dishes, hands, take a shower/bath or flush your toilet ALL of this water goes into your plumbing, into one main drainage pipe that connects directly into your septic tank through the inlet baffle.
Septic tank holds the waste water
The septic tank is a water-tight container that holds the waste water long enough to allow solids to settle down to the bottom (sludge), while the oil and grease float to the top (scum). The T-shaped outlet prevent the sludge and scum from leaving the tank and flowing into the drainfield.
Waste water flows into drainfield
Once the waste water reaches a certain level and leaves the septic tank and flows into the drainfield. The water evaporates and nature removes harmful coliform bacteria, viruses, and nutrients.
Understanding how your septic tank works can help you keep it working properly. Regular maintenance and inspections are important.
The illustration below shows a septic tank needing maintenance, the scum layer is thick and the sludge layer has built up.
To prevent buildup, sludge and floating scum need to be removed through periodic pumping of the septic tank. Regular inspections and pumping are the best and cheapest way to keep your septic system in good working order. — EPA Home Owners Guide