Illinois Home Inspector Exam 2025 – 400 Free Practice Questions to Pass the Exam

The main purpose of a P-trap in plumbing is to hold water and prevent sewer gases from entering the living spaces of a building. A P-trap is a curved section of pipe located under sinks, showers, and other fixtures. When water flows through the trap, it fills the curved portion, creating a barrier that blocks foul-smelling and potentially harmful sewer gases from escaping into the home environment.

This water seal is essential for maintaining indoor air quality and preventing health hazards. While the P-trap connects pipes and plays a role related to the drainage system, its primary function revolves around the water it holds creating this barrier against gases. Other options do not capture the primary role of a P-trap, as filtering solid waste is not a function of the trap itself, and regulating water pressure is controlled by entirely different plumbing systems.