Does the Upside-Down Glass Over the Sink Drain Trick Really Work? A Plumber Explains the Truth

Planning a vacation often means checking off a long list of tasks—locking doors, adjusting the thermostat, unplugging electronics, and making sure your home is safe while you’re away. Recently, a viral travel hack has been making the rounds online, claiming that placing a sheet of paper and an upside-down glass over your sink drain can prevent sewer odors and insects from entering your home while you’re gone.

At first glance, the idea seems strange. Yet, it’s actually based on a real plumbing principle. The problem is that the viral method doesn’t work as reliably as many social media posts suggest.

Before you balance a glass over your sink, here’s what professional plumbers recommend instead.

Why This Viral Sink Drain Hack Became So Popular

The popularity of this travel hack comes from a genuine concern: nobody wants to return home from vacation to unpleasant sewer odors or unexpected pests.

The internet often turns simple household tips into viral sensations, but understanding the plumbing behind the trick helps explain why some methods work—and others don’t.

The Real Plumbing Secret: Your P-Trap

Hidden beneath every sink, bathtub, shower, and many floor drains is a curved pipe known as a P-trap.

Although many people think it simply catches lost jewelry or hair, its primary job is much more important.

The curved section always holds a small amount of water. This water creates a seal that blocks:

Sewer gases
Bad odors
Insects
Small pests

Without that water barrier, air from the sewer system can travel directly into your home.

Why Sewer Smells Can Appear After You Travel

If a drain goes unused for a long period, the water inside the P-trap slowly evaporates.

Once the water disappears, the protective seal is gone.

That’s when homeowners may notice:

Musty or sewer-like odors
Drain flies
Small insects
Unpleasant smells in bathrooms or laundry rooms

Fortunately, this usually doesn’t happen after a short weekend trip.

How Long Does It Take for a P-Trap to Dry Out?

Under normal conditions, most P-traps remain full for several weeks.

However, evaporation happens faster in:

Hot climates
Dry environments
Homes with strong air conditioning or ventilation
Guest bathrooms that are rarely used
Basement floor drains
Laundry room standpipes

If you’re leaving for three weeks or longer, it’s worth taking a few preventive steps.

Does the Paper and Upside-Down Glass Trick Actually Work?

The theory behind the hack isn’t completely wrong.

Covering a drain may slightly reduce evaporation while also creating a partial barrier against odors and insects.

Unfortunately, the execution is where the hack falls short.

A drinking glass simply resting upside down over the drain rarely creates an airtight seal.

The sheet of paper beneath it quickly absorbs moisture, wrinkles, and loses any ability to block airflow.

Even a slight bump can move the glass, making the setup ineffective.

In other words:

The plumbing principle is real. The viral hack isn’t the best solution.

The Right Way to Protect Your Drains Before Vacation

Professional plumbers recommend a few simple steps that are much more reliable.

Step 1: Refill Every P-Trap

Before leaving, run water through every:

Kitchen sink
Bathroom sink
Shower
Bathtub
Utility sink
Floor drain

Allow the water to run for about 10 to 20 seconds.

Don’t forget to flush every toilet as well.

This replenishes the water seal inside each P-trap.

Step 2: Seal the Drain Properly

If you’ll be away for several weeks, consider covering drain openings using:

Built-in sink stoppers
Rubber drain plugs
Silicone drain covers
Plastic wrap
Painter’s tape (temporary solution)

The goal is to reduce evaporation while creating an additional barrier against odors or insects.

Step 3: Add Mineral Oil for Long Vacations

Many experienced plumbers recommend one additional trick.

After running water into the drain, pour about one tablespoon of mineral oil into the drain.

Because mineral oil floats on top of the water, it significantly slows evaporation.

Important: Only use mineral oil.

Cooking oils can become rancid and may contribute to plumbing problems over time.

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Additional Plumbing Tips Before Leaving Home

A few extra minutes of preparation can help prevent expensive surprises while you’re away.

Clean the Garbage Disposal

Food scraps left inside can produce unpleasant odors during your trip.

Check for Frozen Pipe Risks

If you’re traveling during winter, make sure exposed plumbing is properly insulated.

Consider Shutting Off the Main Water Valve

Many homeowners choose to turn off the home’s main water supply before extended vacations.

While optional, this greatly reduces the risk of leaks or burst pipes causing major water damage while no one is home.

Myth vs. Reality

Myth

Placing a piece of paper and an upside-down glass over the sink drain completely prevents sewer odors.

Reality

Unless the cover creates an airtight seal, it provides very little protection.

The most effective solution is keeping the P-trap full of water and sealing drains with proper drain covers or plugs.

Frequently Asked Questions

Do I need to worry if I’m only gone for a weekend?

Usually not. Most P-traps retain enough water for several weeks under normal conditions.

What causes sewer smells after vacation?

The most common cause is evaporation of the water inside the P-trap, allowing sewer gases to enter the home.

Is mineral oil safe for drains?

Yes. Small amounts of mineral oil are commonly recommended by plumbers to slow evaporation during long absences.

Can insects really enter through drains?

Yes. If the water seal disappears, some insects—especially drain flies and small pests—may find their way through plumbing systems.

Should I shut off my home’s water before traveling?

Many plumbing professionals recommend turning off the main water supply during extended trips to reduce the risk of leaks or burst pipes, although it’s not required for every situation.

Final Thoughts

The viral upside-down glass hack isn’t completely based on fiction—it simply oversimplifies a real plumbing issue.

Your home’s P-traps are designed to protect you from sewer gases and unwanted pests, but they only work when they contain water. Before leaving for an extended trip, take a few minutes to refill your drains, seal them properly, and, if you’ll be away for several weeks, consider adding a small amount of mineral oil to slow evaporation.

These simple steps are far more effective than balancing a glass over your sink and can help ensure you return to a home that’s just as fresh and comfortable as when you left.

The Real Deal on Covering Your Sink Before Vacation