What is the purpose of a trap seal in plumbing systems?

• A. Visual barrier between house and soil
• B. Prevents sewer gas from entering living spaces
• C. An insulation barrier
• D. A type of valve

Answer: (B)

The main idea is that a trap seal acts as a barrier to sewer gases. In a drain’s curved section, water sits and forms a seal. That water barrier blocks noxious gases from moving back into the living space, even though waste water and odors are flowing through the pipes on the other side. It’s a passive seal, not an insulation layer and not a valve that controls flow. If the trap dries out or is siphoned away, sewer gases can slip past, which is why keeping the trap filled with water is important. Regular fixture use or a trap primer helps maintain the seal, and proper venting reduces the chance of siphoning. Typical places you’ll find traps are under sinks, in bathtubs or showers, and in floor drains.