Which fixture in plumbing is typically connected to drainage systems?

The water closet, commonly known as a toilet, is the correct answer because it is specifically designed to dispose of waste materials through a drainage system. When a toilet is flushed, it uses water to carry waste away from the fixture into the sewer or septic system, making it a crucial component connected to drainage systems.

In contrast, a faucet primarily serves to control the flow of water for various purposes such as washing hands or filling containers, but it does not contribute to drainage in the same way. A shower, while it does drain water, is typically focused on the delivery of water for bathing rather than waste disposal. Lastly, a water heater provides hot water for various fixtures but does not directly connect to a drainage system itself, as it is usually involved in the supply of water rather than its removal.