A simple travel hack has been circulating online, suggesting that placing a sheet of paper over a sink drain and covering it with an upside-down glass can help block odors and insects while you’re away. It sounds clever—and it’s loosely based on real plumbing science—but experts say it’s not a reliable solution.

The idea connects to a key part of your plumbing system called the P-trap. This U-shaped pipe, located beneath sinks, showers, and tubs, holds a small amount of water. That water acts as a barrier, preventing sewer gases, unpleasant smells, and even small pests from traveling back up through the drain into your home.

When you use your sinks regularly, the water in the P-trap is constantly refreshed. But if a drain sits unused for days or weeks—such as during a vacation—that water can slowly evaporate. In warm or dry conditions, this happens even faster, weakening the protective seal.

At first glance, covering the drain with paper and a glass might seem like a smart backup. However, plumbing professionals point out a key flaw: it doesn’t create an airtight seal. Air, odors, and even insects can still slip through small gaps. On top of that, paper can absorb moisture, become soggy, and lose its effectiveness entirely.

A better approach is to prepare your plumbing properly before you leave. Start by running water through every sink, shower, bathtub, and floor drain to refill the P-traps. This simple step restores the natural barrier your system is designed to use.

For extra protection, you can use built-in drain stoppers or tightly fitting rubber or silicone covers. Some homeowners also place plastic wrap beneath a stopper to create a more secure seal.

If you plan to be away for an extended period, there’s another trick professionals often recommend: adding a small amount of mineral oil to each drain after running the water. The oil floats on top of the water in the P-trap, slowing evaporation and helping the seal last longer.

While the viral hack is based on a real concept, it falls short in practice. Maintaining water in your P-traps and using proper drain covers are far more dependable ways to keep odors and unwanted pests out of your home. Taking just a few minutes to prepare before you leave can make a noticeable difference—and give you peace of mind while you’re away.