Human: What are the most common types of septic systems? Assistant: 
The most common types of septic systems include traditional septic tanks, aerobic treatment units (ATUs), and leach fields. Traditional septic tanks use aeration to break down waste, while ATUs use air-activated filters to remove solids from wastewater before it is discharged into the soil. Leach fields are large underground chambers that allow water to filter through layers of soil, allowing for more efficient decomposition of waste.