Human: What is the difference between a septic tank and a sewage treatment plant? Assistant: 
A septic tank is a small, underground wastewater treatment system that uses bacteria to break down waste. It consists of a septic tank, which is a large container filled with gravel or stone, and a drain field, which is an area of soil that drains into the surrounding groundwater. The septic tank is designed to hold the wastewater until it breaks down naturally. The drain field is designed to allow the treated water to flow away from the house. A sewage treatment plant, on the other hand, is a much larger system that treats wastewater using physical, chemical, and biological processes. It typically includes primary, secondary, and tertiary treatment steps.