Can a dry P-trap make my house smell like sewer gas?
Yes. A trap's liquid seal is what blocks sewer gas from coming back into the house.
Why it happens
Kentucky code defines a trap as a device that provides a liquid seal to prevent sewer gas emission without materially affecting wastewater flow. It also defines trap primers for drains that are used so rarely the trap seal can evaporate.
That is why a guest bath, basement floor drain, utility sink, or rarely used shower can smell after sitting dry. If the smell goes away and stays away after restoring the water seal, the dry trap was likely the issue.
When it is not just a dry trap
Call if the odor is strong, returns quickly, happens at multiple drains, follows gurgling, appears after a sewer backup, or is paired with wet floors. Those symptoms can point to venting, drain, sewer, or floor-drain problems.