Heading 7309 covers containers with a capacity of more than 300 liters (approximately 79.25 gallons). Containers of 300 liters or less classify under heading 7310, which further subdivides by whether capacity is 50 liters or more versus under 50 liters.

Generally, a tank fitted with minor accessories (manholes, valves, level gauges) remains classifiable under 7309 as a container. However, if the tank is an integral part of a more complex apparatus—such as a pressure vessel that is a component of a processing machine—classification may shift to the chapter covering that machinery. The essential character and primary function of the complete article govern the determination.