Which component would a plumber use to connect various bathroom fixtures to a drainage system?

The correct answer is that a plumber would use a sink as part of connecting various bathroom fixtures to a drainage system. The sink acts as a central fixture where water drains from, and it is equipped with a drain assembly that facilitates this connection. Sinks are designed with built-in overflow protection and drainage systems that allow wastewater to be expelled safely into the plumbing system.

In a typical bathroom setup, sinks are a common connection point for various fixtures, allowing waste water from activities like handwashing, tooth brushing, and other hygiene practices to be directed appropriately into the drainage system.

Other listed components serve different purposes in plumbing. A faucet is designed to control water flow from a source but does not play a direct role in drainage. A gas shutoff valve is used to control the flow of gas in a system not related to water drainage, and a flexible gas line is employed specifically for gas distribution. While these elements are essential in various plumbing and utility applications, they do not serve the primary purpose of connecting bathroom fixtures to a drainage system.