Which term describes a plumbing component that must be emptied by mechanical means?

The term that describes a plumbing component that must be emptied by mechanical means is a sump. A sump is typically a pit or reservoir designed to collect water, often from below ground levels, to prevent flooding or to manage groundwater. The collected water needs to be pumped out using a mechanical pump, as it is not gravity-drained.

In plumbing contexts, sumps are commonly used in basements, crawl spaces, and in commercial settings where excess water needs to be handled. They are equipped with a sump pump that automatically or manually removes water when it reaches a certain level.

Other components listed, such as septic tanks, grease traps, and holding tanks, serve different functions and have varying methods of maintenance and emptying. Septic tanks rely on gravity for drainage and are connected to a drain field for treatment; grease traps are typically cleaned as part of routine maintenance but may function through natural drainage over time. Holding tanks, while they do require pumping, may not usually be described purely as emptied by mechanical means. Sumps, however, are specifically designed with pumps to remove collected water, making this choice the best fit for the question.