A tenant in Hong Kong recently experienced a foul odor emanating from a bathroom sink drain, initially mistaken for a smell from towels. Investigation revealed the source to be the sink’s drain and U-trap. A senior building surveyor believes the issue stems from the evaporation of water within the U-trap, allowing sewer gas to enter the bathroom.
Temporary Fixes Fail to Resolve the Issue
The tenant, residing in a low-rise unit in the康怡花園 (Kon Yee Garden) housing estate, had not experienced problems in the first six months of occupancy. The odor arose after returning from a trip to Japan and washing clothes. Attempts to resolve the issue by pouring cleaning agents and hot water into the drain only provided temporary relief, with the smell returning once water flow stopped.
The tenant examined the plumbing and found a U-trap, but was unable to disassemble it for cleaning. Following online advice, they used cleaning agents and drain cleaner, followed by hot water. Despite initial improvement, concerns remained about the odor’s recurrence.
According to certified building surveyor 賴達明 (Lai Da Ming), using cleaning agents or hot water only temporarily masks the odor and doesn’t address the root cause. He warns that strong chemical scents only cover up the smell and high concentrations can damage pipes and cause discomfort.
Three Primary Causes of Drain Odor
Lai Da Ming identified three main reasons for this type of sudden drain odor: failure to install a U-trap during renovations (particularly when converting a bathtub to a shower), a damaged or ineffective U-trap and the drying out of the water seal due to prolonged periods of non-use, such as during travel.
The Importance of a U-Trap
Lai Da Ming emphasized that all household drains should have a U-trap to create a water seal, preventing sewer gas and pests from entering the home. He noted that U-traps come in four main types – U-shaped, S-shaped, bottle traps, and P-shaped – with bottle traps being the most common in Hong Kong residential sinks.
The tenant’s sink uses a traditional U-shaped trap, which is more prone to drying out and causing odors or leaks due to its shallow depth and smaller water capacity.
Potential Solutions
To resolve the odor, Lai Da Ming recommends regularly pouring 500 milliliters of water into the drain to replenish the water seal, a practice also recommended by the Housing Department. Bleach should not be used to avoid environmental contamination. Replacing the U-trap with a bottle trap is also suggested, as it allows for easier physical cleaning. If no U-trap is present, professional installation is strongly advised.
Frequently Asked Questions
What causes the smell from a bathroom sink drain?
The smell is likely caused by sewer gas entering the bathroom due to a dry U-trap, a damaged U-trap, or the absence of a U-trap altogether.
What is a U-trap?
A U-trap is a curved section of pipe under a sink that holds water, creating a seal to prevent sewer gases from entering the bathroom.
How can I temporarily eliminate the smell?
While not a permanent solution, pouring water into the drain can temporarily replenish the water seal and mask the odor.
Do you consider more homeowners should be aware of the importance of maintaining their plumbing’s U-traps?
