What is a "drain plug" in pools?

A "drain plug" in pools is primarily used as a tool to allow for the drainage of water from various components during maintenance. This can include the pool's plumbing or equipment such as filters, heaters, and other accessories. When performing necessary repairs or routine maintenance, having a drain plug enables contractors to ensure that water can be safely and efficiently removed, preventing any potential overflow or spillage during the service process. Properly draining water also protects equipment from damage and ensures a thorough inspection and cleaning of the components.

The other options describe different functions that are not related to the specific purpose of a drain plug. For instance, filtering debris pertains more to various types of pool filters, a safety feature for preventing overflow involves overflow drains or mechanisms, and controlling water circulation relates to valves or pumps. Each of these components has its unique function, but none directly describes the purpose of a drain plug in the context of pool maintenance.