Septic tanks are installed on, with a few exceptions, all septic systems. A septic tank is a dual-chamber, single tank made of either concrete or plastic that accepts raw sewage from the source (your house). Water enters the tank in what is called a baffle, which guides incoming sewage deeper into the tank. This allows the separation of solid material to begin. Heavier types of solids, along with older solids that have been inside the tank a while, sink to the bottom. This layer of solid material is called sludge. The lighter and newer solids float to the top of the tank, which is referred to as scum.

Between the layers of scum and sludge is wastewater that does not hold any solids. This is commonly known as the clear layer. Inside the tank is a hole that separates the two chambers. This partition has about a 4” round hole halfway down. This hole allows the clear water to flow into the next chamber. This chamber stores water that will be dispersed into the drainfield, (sometimes known as the leach field). On the outlet side of the septic tank is another baffle, which serves two purposes: first, the filter inside the baffle prevents any solids that have made it into the second chamber from going out into the drainfield. Second, the baffle serves as a way to draw water from the middle layer and disperse it into the drainfield. This side of the septic tank is supposed to be free of solids, but the baffle acts as insurance.

Over time, sludge layers and scum layers settle, building up into thicker deposits. These deposits are why it is a good idea to pump your septic tank at least once every three years. If these deposits get too thick, they can make their way into the liquid chamber and eventually out into the drainfield, or plug up the filter if one is installed. Solids will plug up the drainfield and prevent it from dispersing water into the ground, causing flooding at the tank and making a mess of the site. 

Click Here to Download the Simply Septic Brochure supplied by DNREC