New Yorkers probably have more experience with odors than the average person. And while identifying those smells can prove difficult at times, it’s important to pinpoint them in certain instances, like in this scenario: There was a bad odor resonating from a kitchen waste-line within an apartment on the eighteenth floor of a residential building in Manhattan. The tenant complained of a bad smell in his kitchen when he awoke. Sometimes rotten garbage that the tenant forgot to remove from his kitchen caused this foul odor, but the actual reason for the odor was fairly typical, and had to do with the plumbing underneath the sink: the seal inside the trap can break and cause the sewage odors to waft out of the waste-lines and into the apartment. If you find you have a similar problem, here’s what you need to ask yourself: why is the water seal inside of the kitchen trap breaking?

A trap, like the one in the photo, is located within a couple feet of each fixture and each drain on a waste-line. The structure of a trap allows water to build up and create a seal within the trap dip (the U shaped part of the trap). The water seal stops the odors from building up inside the waste-lines and seeping into the apartments through the drains. The whole point of installing a trap is to seal the odors inside the waste-lines. If the trap seal were broken, there would be no water in the trap to protect the kitchen from the foul odor of the building’s sewage.

But what causes the water to disappear? Usually the reason for traps not having any water in them is evaporation. But in the case we described, the tenant was home and used his kitchen sink twice a day, so something must have been causing the water inside the trap dip to be pulled from the trap and down the waste-line. As it turns out, there can be another explanation.

In the morning, we typically use a lot of water getting ready for the day. If the vent line for the kitchen sink is clogged, the large amount of water traveling down the main waste stack could cause negative air pressure to form inside the kitchen waste-line. The water inside the trap dip would then be siphoned out, breaking the seal. Maybe you remember learning the laws of fluid dynamics in your bygone days of physics, but basically by the principles of these laws, water is siphoned out of the kitchen waste trap dip where the water seal is located.

When the vent line is clogged, the airflow is restricted and a build-up of pressure inside the waste pipe causes the trap to malfunction. When the water inside the trap is gone, there is nothing to stop the foul odors inside the waste stack from filling the apartment. Only one thing can be done to prevent this from happening: clear the vent line stoppage! Once this happens, the problem will be resolved.

By Spencer Kraus – Account Manager – Fred Smith Plumbing & Heating Co.