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 has at least one family member who swears by unusual household tricks. In my family, that person is my sister. Before leaving on a two-week summer vacation, she asked me to stop by her house every few days while she was away. Her instructions were straightforward—water the plants, collect the mail, and make sure all the doors and windows stayed locked.

As I was getting ready to leave after my final visit, I remembered one last thing she had mentioned: “Before you leave, place an upside-down drinking glass over the kitchen sink drain.”

She insisted it was important but never explained the reason before hurrying off to catch her ride. Wanting to follow her instructions exactly, I did as she asked. Later, though, I found myself wondering why anyone would cover a sink drain with an upside-down glass.

After looking into it and speaking with several home maintenance experts, I learned that this simple habit actually has a very practical purpose.

The Primary Reason: Blocking Unwanted Pests

A house that sits empty for days or weeks can become more appealing to insects and other unwanted visitors. One common reason people cover their drains before traveling is to keep pests from entering through the plumbing.

An Overlooked Entry Point

Drainpipes and sewer lines are dark, damp spaces that contain organic matter, making them an ideal environment for certain insects to live and travel.

Why Vacant Homes Are More Vulnerable

When a home is occupied, running water and daily activity make the plumbing less inviting. However, when sinks go unused and the house remains quiet for an extended period, pests such as cockroaches and drain flies may crawl up through the pipes looking for moisture or food.

An Easy Barrier

Placing an upside-down glass over the drain creates a simple physical obstacle. If insects make their way up the pipe, they reach the covered opening and cannot enter the kitchen, forcing them to retreat.

An Added Bonus: Reducing Sewer Odors

This small trick may also help minimize unpleasant smells while the house is unoccupied.

Under every sink is a curved pipe called a P-trap. It holds a small amount of water that forms a seal between your home and the sewer system, preventing sewer gases from rising into the living space.

If no water is used for an extended period—particularly during hot weather—that water can gradually evaporate. Once the seal is gone, unpleasant sewer odors may begin entering the house.

Covering the drain helps reduce airflow, slowing evaporation while also providing an extra barrier that limits odors from escaping through the drain.

Additional Ways to Protect Your Drains Before a Trip

Many homeowners use a few simple techniques to prepare their plumbing before leaving on vacation. Some popular options include:

• Use a Drain Cover: Place a sink stopper, rubber drain cover, or even a coaster over the drain opening to help create a seal.
• Clean the Drain First: Pour baking soda into the drain, followed by white vinegar, then rinse with hot water to remove buildup and reduce the chance of odors.
• Add Mineral Oil: For longer vacations, pouring a small amount of mineral oil into the P-trap creates a thin layer that slows water evaporation.

Conclusion

What first seemed like one of my sister’s quirky habits turned out to be a smart and practical home maintenance tip. Covering a kitchen sink drain with an upside-down glass is a quick, inexpensive way to help keep insects out and reduce the chance of unpleasant odors while you’re away.

If you’re planning to leave home for several days or longer, this simple trick may be worth including on your pre-vacation checklist.