You’re packing your bags, checking the doors, turning off appliances—and then someone tells you to put a piece of paper over the sink drain and place a glass upside down on top of it.

At first, it sounds completely strange.

But there is a real plumbing reason behind the idea. The important part is understanding what the trick can and cannot actually do.

🚰 The Secret Is Under Your Sink

Every sink normally has a curved section of pipe called a P-trap.

That curved pipe is designed to hold water. The water creates a barrier between your home and the drainage system, helping prevent unpleasant sewer odors from traveling back through the drain. (oatey.ca)

When you use your sink regularly, fresh water continually replenishes this trap.

But when a home sits unused for a long period, especially in a hot or very dry environment, the water in a rarely used trap can gradually evaporate.

Once that water seal disappears, odors can potentially travel through the drain.

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🦟 Could Bugs Come Through the Drain?

A dry drain can also provide an easier route for certain insects and other unwanted pests.

That is one reason people sometimes cover drains when leaving a property empty for an extended period.

However, the P-trap itself is normally the primary barrier, not the upside-down glass. (Remèdes Maison Faciles)

So the viral trick shouldn’t be thought of as a magical replacement for proper plumbing.

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🥛 So What Is the Glass Supposed to Do?