S-traps are no longer allowed in new construction
Years ago most plumbing codes banned S-trap configurations in favor of P-trap style fixtures. S-traps are no longer used in modern plumbing because on rare occasions with just the right conditions the water can be sucked out of the trap allowing sewer gas to enter your home.
The risk from sewer gas can be much worse than just that terrible smell. Sewer gases can be poisonous or even explosive and are not to be treated lightly. Continue reading S-Traps vs P-Traps