A dip tube (or withdrawal tube) is fitted internally to the valve of a cylinder or drum tank. Dip tubes are used for liquid phase product withdrawal from cylinders of liquefied products such as liquid hydrocarbon blends, carbon dioxide, propane, ammonia or various refrigerants. The dip tube runs down the centre of the pressurised cylinder and draws the liquid up through the valve. A dual port valve can also be used in combination with a dip tube when additional head space pressurisation is required to remove the liquified product, or it can allow the product to be withdrawn in either liquid phase with the dip tube or through the vapour port.