S-Trap vs. P-Trap: What’s the Difference?
The plumbing trap beneath your sink plays an important role in protecting your home from unpleasant and potentially harmful sewer gases. While P-traps are the modern standard, older homes may still have S-traps, which can create plumbing problems.
An S-trap has a tendency to siphon water out of the trap after the sink drains. When this happens, the water seal is lost, creating an open path for sewer gases to travel through the drain and into your home.
A P-trap, on the other hand, is designed to retain a small amount of water after each use. This standing water forms a seal that blocks sewer gases while still allowing wastewater to flow freely into the drain system.
Even if your home has properly installed P-traps, the water inside them can evaporate if a sink, floor drain, or other plumbing fixture goes unused for an extended period. To maintain the protective water seal, it is recommended to run water through all plumbing fixtures at least once a month, especially in guest bathrooms, vacation homes, or infrequently used areas.
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