What should portable DOT containers designed to be filled by weight be marked with?

Portable DOT containers designed to be filled by weight must be marked with the water capacity in pounds because this measurement directly correlates with how propane and similar gases are typically weighed for filling purposes. Since the weight of the liquid propane is what determines how much can be safely stored and transported, understanding this weight in pounds facilitates compliance with safety regulations and proper refilling practices. This marking is essential for users to ensure that they do not overfill the containers, which can lead to dangerous situations such as leaks or pressure build-up. Other options, while relevant to other contexts, do not reflect the standard measurement used for weight-based filling of these containers, making them less practical for this purpose.