Why do buildings not smell like sewers even though waste is flushed down the toilet or washed down the sink? The reason is that the installed ventilation pipes and p-traps in the building’s plumbing. Since water is not constantly flowing, the sanitary pipes will dry and the waste inside will decompose and give off sewer gases and unwanted odors. That is why buildings have vents in roofs for this waste gas to escape from, and p-traps located under plumbing fixtures prevent sewer gases from entering the building.
How do P-traps Work?
P-traps retain fluid in its bend to create a water seal that acts as a gas barrier. The image above demonstrates how the gases get repelled. One concern with p-traps is the water seal evaporating and allows the sewer gas into the building. Running water through the fixture prevents the water seal from evaporating. If it has evaporated, running water for a few minutes will refill the p-trap and recreate the water seal. It is common to see cold-water primers installed in conjunction with floor drains for this same purpose.
Another concern is siphoning or blowing out the water seal from poor ventilation. Maintaining atmospheric pressure within the drain lines prevents this from occurring. Unequal air pressure siphons the water toward the section of the pipe with the lower pressure. Ventilation is required a certain distance from each fixture guided by the area plumbing code.
Designing plumbing drain, waste, and vent systems to the local area plumbing code ensures proper prevention of these sewer gases from entering the building. Broadtrade Service Group is familiar with constructing and correcting DWV systems. Contact us to ensure buildings do not end up smelling like a garbage chute.