Not all septic systems are the same and actually no two septic systems are the same! Even if two septic systems were installed by the same installer and are built with the same parts, once wastewater goes in they start to function based on the contents and unless the same wastewater goes into both they start to differ as they mature. Phew! Now that we have that out of the way, in theory all septic systems have the same goal which is to provide the user with a way to safely dispose of wastewater. Septic systems perform the same basic functions which are to process waste and then dispose of the excess water but depending on the components this can be done in different ways. In order to better describe a septic system it is sometimes simpler to view the system as a series of functions that are performed. It accomplishes this in several steps which vary depending on the type of septic system.
The first step is usually the separation of solids that are not biodegradable. The primary method for this separation is gravity and time. Given a large enough tank capacity it will take long enough for the wastewater to move through that gravity will have enough time for the separation to take place. After separation takes place then it is time for the treatment and disposal of the wastewater. Below are a list of components that might be used on a given septic system depending on many factors some of which being the capacity or size required and local regulatory rules.