A trash tank is similar to a septic tank in design and is generally used before advanced treatment units (ATU). These tanks can be as small as one-half of the daily design flow volume. The size is generally specified by the manufacturer of the ATU. Trash tanks can serve as an anaerobic or facultative treatment device, but mainly serve to remove plastic and other non-degradable items from the wastewater stream. Trash tanks are not designed for recirculation.