Furnace Fiascos Avoided

Common Causes Of Water Loss In Your Plumbing Fixture Traps

Every plumbing fixture in your home should have a trap between the fixture and drain line. This trap, which maintains a small volume of water that blocks the passage out of the fixture, serves to prevent foul-smelling sewer gas from entering your home. While it isn't usually harmful, the odor is unpleasant and can even cause eye and respiratory distress. That is why having a functioning trap is important. Unfortunately, plumbing traps sometimes lose their water for various reasons, thus opening your home up to gas seepage. Here are some of the most common causes of trap water loss:

Missing or poor venting

When you flush a toilet or drain water from a sink or tub, then there should be venting in the system to permit the effluent to flow smoothly into the drain line. Much like a bottle turned upside down will drain its contents in gurgling "fits", a clogged or missing vent will disrupt the flow of effluent. In some cases, the gurgling can become so violent that the trapped water is evacuated. That is why the installation of a proper vent or removal of a clog inside a vent pipe is essential to maintain smooth flushing and draining. If you aren't able to determine if your fixtures are vented properly, then you will need the services of a plumber to perform an inspection.

Wind-induced oscillation

Another phenomenon that can cause a trap to lose water is oscillation due to high wind speeds. As the wind blows at a significant velocity, it will push and pull air through the vent pipe as it exits the roof. This back-and-forth movement also causes the water inside the trap to slosh back-and-forth, or oscillate. If oscillation exceeds a certain point, then it can cause the water to slosh out of the trap. Preventing oscillation may require the use of a special one-way cap to block air flow into the vent pipe, if the problem occurs often.

Obsolete trap design

Traps have been manufactured in a variety of configurations over the years, but some styles are deemed obsolete due to design flaws. One such design is the S-trap, which consists of an S-shaped section of pipe. In some circumstances, the high drain velocity of the effluent can siphon the water from the trap. That is why a P-trap, which contains a horizontal, straight section of pipe that slows down water flow, is preferred over S-traps. It is beneficial to inspect your plumbing fixtures to check for obsolete trap designs or hire a plumber to perform this inspection for you. In many cases, plumbing traps can be replaced quickly and easily by a qualified professional.

Capillary evacuation

Another way for a plumbing trap to lose its water is by capillary action. This occurs whenever an object extends from the trap to the drain pipe. In the same manner that liquids are drawn up a wick, the water in the trap can be drawn out of the trap along this object. Items such as dental floss, string, or even hair can cause capillary evacuation of the trap. That is why you should keep debris from entering your drains through the use of strainers and also periodically check your drains for buildup.


Yet another way for water to leave your trap high-and-dry is evaporation of the water. This can occur whenever a plumbing fixture sits undisturbed for a lengthy period of time, and the water inside the trap simply evaporates. This problem can become worse during the dry, winter months or if the air conditioner is being used extensively in summer. That is why it is important to regularly flush unused toilets or run faucets in sinks that are not often utilized.

For more information, contact a plumber at a company like C B Lucas Heating & Air Conditioning.