The large TOTO Sub-Tank for the Auto Soap Dispenser is designed to hold 5.3 gallons (20 liters). This large reservoir helps minimize frequent refills and helps ensure proper function of the Auto Soap Dispenser. This sub-tank is designed to hold TOTO Green Seal,oap and compatible to the Auto Sensor Soap Dispenser. Additional 20 liter sub-tank allows for longer lasting supply. Helps ensure proper function of the Auto Soap Dispenser. For use with TOTO Biodegradable, Green Seal,oap (#TSFB) required. Includes 20 liter (5.3 gallon) sub-tank only