4.5 Gal. Thermal Expansion TankEasyFlex Tankone is designed to maintain safe pressures in a domestic water heating system that utilizes a backflow preventer or check valve. Tankone features a butyl rubber diaphragm and plastic liner to separate the system water from the tank's air charge. The system connection has a stainless steel nipple to prevent corrosion. High quality coating on the shell will help to prevent external corrosion. Every Tankone tank is comprehensively tested and