What is meant by fixture drain in plumbing?

A fixture drain refers to the drain that extends from a fixture's trap to a junction or a vertical stack. This component serves as the essential pathway for wastewater and sewage to flow from the fixture to the building's drainage system. It typically includes the trap, which is designed to prevent sewer gases from entering the living space while allowing wastewater to pass through. The function of the fixture drain is crucial as it connects the individual plumbing fixtures, such as sinks, toilets, and showers, to the broader plumbing system.

The other choices do not accurately describe a fixture drain. Connecting a fixture to the main water supply pertains to the water supply line, not the fixture drain. The pipe that drains water from a building to the sewer relates to the building sewer rather than the internal fixture drain. The section of pipe connected to the water heater addresses the hot water supply rather than drainage. Understanding the role of the fixture drain helps in comprehending plumbing systems and their functionality.