A sewer gas odor that appears exclusively at night is typically caused by thermal dynamics, shifting barometric pressures, and increased nighttime plumbing usage. As outdoor temperatures drop after sunset, air pressure changes can pull sewer gases up through dry P-traps or minor pipe leaks. Furthermore, when family members take evening showers or run laundry late at night, the sudden rush of wastewater can siphon water out of vulnerable P-traps or force trapped gases out of restricted roof vents, making nighttime odors much more noticeable. Verification: Check all P-traps and roof vent stacks to ensure proper barometric pressure equilibrium and trap water levels.
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