The P-trap is now the standard since the S-trap was deemed ineffective and prohibited in new construction under the Universal Plumbing Code. The S-trap was found to be prone to siphoning and drying out, which leaves the apparatus ineffective.
The Difference
The difference between the two traps is simple: the shape. An S-trap flows down from the drain, curves up, then curves back down. The P-trap also flows down from the drain and curves, but the curve finishes on a horizontal pipe that takes the waste out.
Once the trap dries out, sewer gases can start flowing back into your home. The quick fix is to run some water to recreate the seal. If you have an S-trap installed and frequently smell sewer gases in your home, consult with our plumbing team about switching to a P-trap.