House Sewer line – Line connecting plumbing from house to septic tank. Septic tank – Household waste receives primary treatment in the septic tank, an anaerobic environment, and separates into 3 layers; a sludge layer, a clear zone, and a scum layer. Solids heavier than water settle on the bottom to form the sludge later. The clear zone contains mostly brown, murky water made up of biodegradable and non-biodegradable material. The scum layer that forms on top contains materials lighter than water including, fats, oils, grease, and soap scum. Bacteria break down some material in this layer that then becomes heavier and sinks to the sludge layer. Waste enters the tank through an inlet baffle or tee that promotes proper mixing and ensures materials in the scum layer do not enter the inlet line. Water from the clear zone exits the tank through an outlet baffle or tee that is set at a level below the inlet ensuring waste and water flow in one direction through the tank and that materials from the scum layer do not discharge to the drain field through the outlet. An effluent filter may be present in the outlet baffle of the tank for additional treatment. Distribution Box – The distribution box is generally a smaller concrete or plastic box that distributes the effluent flow evenly to the drain lines and if in balance, ensures that no single drain line or area of the absorption field is overloaded. Absorption Field – The absorption field most commonly, in conventional systems, is a design of trenches using a system of gravel and perforated pipe or a gravel-less technology, such as EZ flow or Infiltrators. As effluent is discharged through these pipes it filters through the soil and is further treated and bacteria filtered out.