A simple travel hack has been circulating online that suggests placing a sheet of paper over a sink drain and covering it with an upside-down glass. The idea is supposed to keep unpleasant odors and insects from entering while you’re away. While the trick is loosely based on real plumbing science, experts say it is not a dependable solution.

The real protection comes from the P-trap, the U-shaped pipe beneath sinks, showers, and tubs. It holds water that blocks sewer gases, bad smells, and small pests from coming back through the drain. However, when a drain is unused for days or weeks, especially in warm or dry conditions, the water can slowly evaporate and weaken that barrier.

Covering the drain with paper and a glass may seem like a useful backup, but it does not create an airtight seal. Air, odors, and insects can still get through small gaps, while paper can absorb moisture and become ineffective. As the original article explains, “it doesn’t create an airtight seal.”

A more reliable solution is to run water through every sink, shower, bathtub, and floor drain before leaving. This refills the P-traps and restores the plumbing system’s natural barrier. For additional protection, tightly fitting drain stoppers or rubber and silicone covers can help seal openings.

For longer trips, some professionals recommend adding a small amount of mineral oil after refilling the P-traps. The oil floats on the water and can slow evaporation, helping the protective seal last longer. In the end, the viral paper-and-glass trick is based on a real plumbing principle, but proper preparation is much more dependable. A few minutes of preparation before vacation can help keep your home fresher and reduce the chance of unwanted odors or pests.