My sister left for vacation and asked me to place an upside-down glass over her kitchen sink drain before I left. She said it was important but never explained why. I did it but now I’m curious: what was it for?

Everyone seems to have a relative with a few unusual household habits they swear by. In my family, that person is my sister. Before leaving for a two-week summer trip, she asked me to keep an eye on her house while she was away. The instructions were pretty typical—water the plants, bring in the mail, and double-check that everything was locked up.

Just as I was about to leave on the last day, I remembered one final request she had made: “Before you go, put an upside-down glass over the kitchen sink drain.”

She stressed that it was important but never had time to explain why before rushing off to catch her ride. Wanting to follow her instructions exactly, I did it without question. Still, once I got home, I couldn’t stop wondering what purpose a simple drinking glass could possibly serve sitting upside down in a sink.

After researching the idea and talking with a few home care professionals, I discovered that this surprisingly simple trick actually serves a very practical purpose.

The Main Benefit: Keeping Unwanted Pests Out

A quiet, empty house can become an attractive place for insects and other unwanted visitors. One of the main reasons homeowners cover drains before traveling is to stop pests from using plumbing as an entry point.

A Hidden Pathway

Drainpipes and sewer systems are dark, damp environments filled with organic material, making them ideal habitats for insects.

Why Empty Homes Are Different

When people are home, regular water use and activity help discourage bugs from exploring the plumbing system. But when faucets go unused and the house sits still for days or weeks, insects such as cockroaches and drain flies may travel upward through the pipes in search of food or moisture.

A Simple Physical Barrier

An upside-down glass creates a solid cover over the drain opening. Any insects that make their way up the pipe encounter an obstacle they can’t get past and are forced back down.

Another Advantage: Preventing Musty Sewer Odors

The trick can also help reduce unpleasant smells from developing while the house sits vacant.

Beneath every sink is a curved section of pipe known as a P-trap. Its purpose is to hold a small amount of water that acts as a seal between your home and the sewer system, preventing gases from traveling back into the house.

During long periods without water use—especially in warm weather—that water can slowly evaporate. If the seal disappears, unpleasant odors may begin drifting into the kitchen.

Covering the drain helps slow evaporation and adds another barrier that keeps odors contained within the plumbing system.

Other Helpful Drain Protection Tips Before Traveling

Homeowners have used similar methods for years to prepare their homes before vacations. Some alternatives include:

• Drain Stopper Method: Place a sink stopper, coaster, or rubber cover over the drain opening to create a seal.
• Baking Soda and Vinegar Cleaning: Pour baking soda followed by white vinegar down the drain before rinsing with hot water to remove food residue and reduce odors.
• Mineral Oil Technique: For longer trips, adding a small amount of mineral oil to the P-trap can create a protective layer that slows water evaporation.

Final Thoughts

My sister’s unusual request turned out to be surprisingly practical rather than overly cautious. Covering a sink drain with an upside-down glass is an easy, inexpensive step that may help prevent pests and unwanted odors while you’re away.

The next time you’re preparing for a vacation, this simple trick might be worth adding to your own pre-trip routine.