We’re Going on Vacation, and My In-Laws Told Me to Cover My Sink Drain with a Piece of Paper and Place a Glass Upside Down Over It. I Didn’t Want to Seem Ignorant by Asking, but I’m Really Curious. Does Anyone Know Why?

If you’ve never seen this trick before, you’re definitely not alone. At first glance, placing a sheet of paper over a sink drain and covering it with an upside-down glass seems like an odd thing to do before leaving for a vacation. Yet many homeowners have learned this simple habit from parents, grandparents, or experienced travelers.

So, what’s the idea behind it?

The main purpose is to create an extra barrier over the drain while the house is empty. Although your plumbing already includes a P-trap—the curved section of pipe that holds water to block sewer gases—some people like adding another layer of protection if they’ll be away for an extended period.

Here are some of the reasons people use this trick:

• Helps discourage insects: Insects such as drain flies, cockroaches, or other small pests can sometimes travel through plumbing systems, especially if a drain dries out. Covering the drain may make it more difficult for them to emerge into the sink.
• Reduces odors: If the water in the drain trap slowly evaporates during a long absence, unpleasant sewer odors could enter the home. While the glass itself won’t stop evaporation completely, it may slightly reduce airflow over the drain.
• Keeps dust and debris out: An upside-down glass prevents dust, crumbs, or small objects from accidentally falling into the drain while you’re away.
• Provides peace of mind: Sometimes family traditions continue simply because they’ve worked well over the years. Even if the practical benefit is small, many people appreciate taking a few extra precautions before leaving home.

However, it’s worth noting that this method is not considered a standard recommendation by plumbing professionals. If you’ll only be away for a few days, there’s usually no need to cover the drain.