Consisting of a septic tank, drain lines, drainfield, and other components, your septic system is responsible for drawing and treating wastewater from your home. Wastewater flows into the tank, where solids form a sludge at the bottom, and oil, grease, and other lighter materials float to the top. The leftover liquid, called effluent, flows into the drainfield to percolate in the soil, which naturally filters out bacteria, pathogens, and nutrients.