NCCER Plumbing Level 2 Practice Exam 2026 - Free Plumbing Certification Practice Questions and Study Guide

The primary function of a trap in a plumbing system is to block sewer gases from entering living spaces. Traps are designed as a curved section of pipe that holds a small amount of water, creating a seal. This water barrier prevents harmful and odorous gases produced in the sewer lines from flowing back into the home or building.

Traps are an essential component of drainage systems, ensuring health and safety by mitigating the risks associated with sewer gas exposure. They also play a role in preventing vermin from traveling into structures through the plumbing, as the water seal obstructs their path. The effectiveness of traps depends on their proper design and installation, which is critical in maintaining both functionality and sanitary conditions within a plumbing system.