What type of tank is used for holding human waste on ships?

The VCHT (Vacuum, Collection, Holding, Transfer) tanks are specifically designed for managing human waste on ships. These tanks utilize a vacuum system to collect waste from onboard toilets, ensuring that it is safely stored until it can be properly processed or disposed of in accordance with marine environmental regulations. The design is tailored for efficient collection and holding, minimizing the risk of leaks or contamination in the ship's environment.

In contrast, potable water tanks are intended for storing drinkable water, while bilge tanks collect excess water from the ship, such as rainwater or seawater that has entered lower compartments. Overflow tanks are used to prevent spillage from other types of tanks by providing a space for liquid once the main tank reaches capacity. Each of these alternatives serves different purposes and is not suitable for the specific needs of holding human waste, which is why the VCHT tank is the correct answer.