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:
- The water in that plumbing trap sits completely still.
- 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:
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:
1. The Dreaded Sewer Gas Smell
Without a barrier, evaporating P-traps allow methane and sewer gases to seep into your home. There is nothing worse than opening your front door after a relaxing vacation only to be hit with a wave of a foul, rotten-egg odor that has been building up in an enclosed house for days.
2. Uninvited Pest Invasions
A dry drain line is an absolute paradise for creepy-crawlies. Drain flies, fruit flies, and sewer roaches are constantly looking for moisture and organic matter. When the water barrier disappears, they will happily crawl up the pipes and make themselves at home in your empty kitchen. The weight of the upside-down glass ensures they are completely trapped beneath the sink line.
How to Do It Right Before Your Next Trip
If you want to adopt this brilliant, zero-cost trick for your next getaway, the process takes less than thirty seconds.
1
Run the water
1 min
Before turning off the lights, run the kitchen and bathroom faucets for 10 seconds to ensure the P-traps are completely full of fresh water.
2
Lay the barrier
1 min
Place a small piece of thick paper, a wax paper square, or a piece of plastic wrap flat over the drain mesh.
3
Weight it down
1 min
Place a heavy glass or coffee mug completely upside down over the paper, ensuring it covers the entire circumference of the drain hole.