There are countless home hacks that suddenly become popular online, especially when vacation season arrives. One of the more unusual ones involves covering your sink drain before leaving home, sometimes with a sheet of paper and an upside-down glass. The idea sounds strange at first, but it is based on a real plumbing concern: what happens when a drain sits unused for an extended period?
The basic reasoning has some truth behind it. The curved pipe underneath most sinks, known as a P-trap, is designed to hold water. That water creates a seal that helps keep sewer odors and gases from traveling through the drain and into your home. It can also discourage insects and other small pests from coming through the plumbing.
However, the viral paper-and-glass trick isn’t the most reliable way to protect your home.
The important part isn’t really the glass sitting over the sink. It’s the water inside the plumbing beneath it.
Understanding how that water seal works—and what you should actually do before leaving for a trip—can save you from returning home to unpleasant odors or plumbing surprises.
Why Does a Sink Have a Curved Pipe?
If you’ve ever looked underneath a sink, you’ve probably noticed the curved section of pipe beneath the drain.
That curve is the P-trap.
Although it may look like an unnecessary bend in the plumbing, it serves a very important purpose. Water remains inside the curved portion after you use the sink, creating a barrier between your home’s drainage system and the larger sewer system.
That small amount of water is commonly called a water seal.
It helps prevent sewer odors from traveling backward through the drain and into your kitchen, bathroom, or laundry area.
Without that water barrier, unpleasant smells could potentially move directly through the drainage pipes.
The P-trap therefore isn’t simply there to catch objects that accidentally fall down the drain. Its water seal is an essential part of the plumbing system.
What Happens When a Drain Isn’t Used?
Normally, every time you run water through a sink, shower, bathtub, or other drain, the P-trap gets replenished.
But when a drain remains unused for a long period, the water inside it can gradually evaporate.
Once enough water disappears, the protective seal becomes weaker or disappears completely.
That’s when problems can develop.
You may return from a long trip and notice that a bathroom or spare room smells strangely like sewage. In some situations, the problem can be traced back to a dry drain trap.
This is particularly relevant for drains that aren’t used regularly.
A frequently used kitchen sink is constantly receiving fresh water, while a guest bathroom, basement floor drain, laundry drain, or rarely used shower may sit untouched for weeks.
Why Do People Cover the Sink?
The idea behind covering a sink before vacation is fairly simple.
If evaporation is the concern, placing something over the drain might seem like a logical way to slow it down.
The viral version of the hack often involves putting paper over the drain and then placing an upside-down glass over it.
The concept is that the covering could create another barrier between the drain opening and the room.
There is a small amount of logic behind this. Covering a drain can potentially reduce exposure to air and provide an additional physical barrier.
But there is an important distinction between covering a drain and creating an airtight seal.
Simply placing an upside-down glass over a sheet of paper doesn’t guarantee that the drain is sealed.
If air can move around the edges, the setup isn’t a dependable barrier.
The Glass Isn’t the Main Protection
This is where the viral trick can be misleading.
The most important protection is already built into the plumbing.
It’s the water sitting inside the P-trap.
If the trap remains full, it already provides a barrier against sewer gases and odors.
An upside-down glass sitting in the sink basin doesn’t replace that water seal.
And if the trap eventually dries out, a loosely positioned glass may not provide the kind of airtight barrier people imagine.
The underlying plumbing is therefore much more important than what you place on top of the sink.
Does the Paper-and-Glass Trick Actually Work?
Not reliably.
If the glass does not create a tight seal around the drain, odors or gases can potentially move around it.
The paper itself is also not a particularly durable plumbing solution. Moisture, movement, or accidental contact could disturb the setup.
So while the idea comes from a real concern—protecting an unused drain—the viral method isn’t something homeowners should depend on as their primary defense.
A better approach is to make sure the P-trap is properly filled before leaving and, for extended absences, use an appropriate drain stopper or cover designed for that purpose.
How Long Does a P-Trap Stay Full?
There isn’t one universal timeframe.
How quickly water evaporates depends on several factors, including temperature, humidity, ventilation, airflow, and the particular drain.
A drain in a warm, dry, well-ventilated area may lose water faster than one in a cool, humid room.
That’s why a rarely used drain can sometimes develop odors even when the rest of the home’s plumbing is perfectly fine.
A short weekend trip generally isn’t the same situation as leaving a property vacant for many weeks.
The longer the absence, the more worthwhile it becomes to think about rarely used drains.
Which Drains Deserve Extra Attention?
Don’t focus only on the kitchen sink.
Before a longer vacation, consider every drain that normally receives little water.
These can include:
- Guest bathroom sinks
- Guest showers
- Bathtubs
- Basement floor drains
- Laundry-room drains
- Utility sinks
- Rarely used bathroom drains
- Other floor-level drains around the home
A floor drain in a basement or utility room can be especially easy to forget because it may not be part of your everyday routine.
The Simple Step to Take Before Leaving
One of the easiest things you can do before leaving home is run water through the drains.
Turn on each sink and let water flow for a short period.
Run the shower or bathtub as well.
If you have drains that aren’t regularly used, make sure their traps receive enough water to replenish the water seal.
This is far more important than balancing an upside-down glass over a piece of paper.
The goal is simple: make sure the P-traps contain water before you leave.
Don’t Forget the Toilets
Toilets also rely on water to create a barrier between your home and the drainage system.
Before leaving, flushing toilets as part of your normal pre-trip routine ensures their bowls and traps contain water.
If you have a bathroom that hasn’t been used for some time, it is especially easy to forget about it.
A quick inspection before locking the door can prevent unpleasant surprises later.
What About a Drain Stopper?
For an extended absence, an actual drain stopper or purpose-made drain cover can make more sense than a sheet of paper.
A properly fitting stopper can reduce airflow through the drain opening and may also help limit evaporation.
Some silicone drain covers are designed specifically to sit over drains and provide a more secure barrier.
If you already have a sink stopper, simply closing it before leaving is another straightforward option.
The exact solution depends on the type of drain and the length of your absence.
Be Careful With Homemade Drain Seals
It’s tempting to improvise with plastic bags, tape, paper, or household objects.
But not every homemade solution is a good idea.
You don’t want something to fall down the drain.
You also don’t want adhesive residue left around plumbing fixtures or a covering that becomes trapped or difficult to remove.
If you want to physically cover a drain, use something that is designed for that purpose and can be removed easily.
What About Mineral Oil?
You may also encounter advice recommending that homeowners pour a small amount of mineral oil into a rarely used drain after filling the trap.
The theory is that oil floats on top of the water and can slow evaporation.
This is a technique sometimes discussed for maintaining water seals in certain situations, but it isn’t necessary for an ordinary short vacation, and homeowners should be cautious about putting substances down drains without knowing whether they are appropriate for their plumbing or local wastewater system.
Most people don’t need an elaborate treatment for a normal trip.
Simply keeping traps filled and using appropriate drain covers is usually a much more straightforward approach.
And don’t substitute cooking oil for plumbing-related purposes. Food oils can become rancid and may create their own plumbing problems.
