<human>: What are the most common types of septic tanks and how do they work?
<bot>: The most common types of septic tanks are gravity-fed, pressure-assisted, and vacuum-composting. Gravity-fed systems rely on the force of gravity to move liquid waste into the tank where it is broken down by bacteria before being released into the soil. Pressure-assisted systems use a pump to help draw wastewater into the tank and then release it at a higher elevation than gravity alone would allow. Vacuum-composting systems use a pump to create suction that pulls air from the tank, creating an environment for anaerobic digestion. All three systems have their own advantages and disadvantages, but in general, gravity-fed systems are considered more cost-effective while vacuum-composting systems provide better treatment of wastewater.