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?

We’ve all been there: you’re packing your bags, double-checking the locks, and rushing to get out the door for a well-deserved vacation. But right before you leave, an older relative or in-law drops a piece of advice that sounds entirely unhinged.

A perplexed traveler recently shared a dilemma that has since sparked a massive wave of curiosity across home-hacks forums: “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 heard of this trick, it sounds like a superstitious old wives' tale. But it turns out, this old-school domestic hack is rooted in pure, practical science. Here is exactly why your in-laws are plumbing geniuses.

The Culprit: The Evaporating "P-Trap"

To understand why a glass and a piece of paper can save your kitchen, you have to understand how your plumbing works. Directly underneath every sink in your house is a U-shaped pipe called a P-trap.

Under normal circumstances, that curve always holds a small amount of standing water. That water acts as a crucial, airtight seal between your living space and the city sewer line. When you are home using the sink every day, that water is constantly refreshed.

But when you go on vacation for a week or two, two things happen:

1. The water in that plumbing trap sits completely still.

2. Depending on the humidity in your home, that water can begin to evaporate.

Once the water level drops too low, the invisible barrier is broken. This opens a direct highway from the sewer line straight up through your kitchen drain.

The Two Disasters This Hack Prevents

By placing a piece of paper (or a small square of cardboard/plastic wrap) over the drain opening and sealing it tightly with a heavy, upside-down drinking glass, you are creating an artificial backup seal. This protects your home from two major vacation nightmares:

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