In a plumbing system, which component is essential for proper drainage?

Traps play a crucial role in a plumbing system's drainage functionality. They are designed to hold a small amount of water, which creates a seal that prevents sewer gases from entering the living space while allowing wastewater to flow through. This seal is essential for the safe and effective removal of waste from fixtures like sinks, bathtubs, and toilets.

While other components like vent pipes, cleanouts, and valves all contribute to the overall effectiveness and maintenance of a plumbing system, traps are specifically required to ensure that drainage occurs without backflows of unpleasant odors or gases into the building. Vent pipes provide necessary airflow that keeps the system functioning efficiently, cleanouts allow for easy access to remove obstructions, and valves manage the flow of water but do not directly impact the drainage process in the same way that traps do. Thus, the primary function of proper drainage relies heavily on the effectiveness of traps in a plumbing system.