When a drain is used regularly, the water in the P-trap is constantly refreshed. However, if a sink or other fixture goes unused for an extended period—particularly during a long vacation—the water can gradually evaporate. This process happens more quickly in warm, dry environments, reducing the effectiveness of the water seal.
Some people believe covering the drain with paper and an upside-down glass can solve the problem. While it may appear to add an extra layer of protection, plumbing experts note that the method is unlikely to create an airtight seal. Without a secure seal, odors or insects may still find their way through the drain. In addition, paper can absorb moisture, become damp, and lose its ability to cover the opening effectively.
A more reliable approach is to prepare your plumbing before leaving home. Running water through every sink, shower, bathtub, and floor drain helps refill the P-traps and restore the protective water barrier. Afterward, using built-in drain stoppers or properly fitting rubber or silicone drain covers can provide additional protection. Some homeowners also use plastic wrap beneath a drain stopper to create a tighter temporary seal.
