Our cylinder tanks are DOT-APPROVED 4BA-400 cylinders. Each cylinder is equipped with an internal liquid siphon dip tube with 1 liquid port (red) and 1 vapor port (blue). The red port is attached to the internal liquid siphon dip tube. The size and type of the valve connections are 1/4″ male SAE flare fittings. These cylinder tanks are refillable and are part of our EZ Exchange Program.