What is the primary purpose of a plumbing trap?

The primary purpose of a plumbing trap is to prevent sewer gases from entering a building. A trap is a curved section of pipe that holds a small amount of water at all times. This water acts as a barrier between the interior of the building and the sewer system. The water in the trap effectively blocks the passage of odors and harmful gases that can emanate from the sewage system, thereby protecting the inhabitants of the building from potential health hazards associated with these gases.

While options like preventing water leakage, allowing air ventilation, and regulating water pressure are important aspects of plumbing systems, they do not pertain to the specific function of a plumbing trap. Traps are not designed to handle water leaks, facilitate air movement, or manage water pressure; their singular and crucial role is to provide a seal that keeps harmful sewer gases contained.