Which method is not suitable for tank cleaning?

Using water from a local source is not suitable for tank cleaning because the water may contain impurities, sediments, or contaminants that can compromise the cleanliness of the tank and the integrity of its previous cargoes. This method poses a risk of introducing foreign substances into the tank, which can lead to contamination of future loads, especially when dealing with different types of cargo or sensitive materials.

In contrast, other methods such as chemical washing with non-toxic agents, mechanical scrubbing, and steam cleaning are specifically designed to effectively remove residues and contaminants from tank surfaces. They utilize controlled methods and appropriate cleaning agents to ensure a thorough and safe cleaning process, thus maintaining the quality of the tank for subsequent use.