It may look like a strange household ritual, but covering a sink drain before leaving home for several days can have a practical purpose. The idea is mainly related to odors, insects, and the water barrier inside the plumbing system.
The drain underneath a sink is connected to a plumbing trap, commonly called a P-trap. This curved section of pipe is designed to hold a small amount of water. That water acts as a barrier between the living space and the drainage system.
When the plumbing is functioning normally, the water inside the trap helps prevent unpleasant sewer gases from traveling back through the drain and into the kitchen or bathroom.
The problem is that if a home is left empty for a long time, water in some traps can gradually evaporate. This is particularly possible in warm, dry conditions or when a drain is rarely used.
Once the water seal becomes weak or disappears, odors from the drainage system can potentially enter the room.
This is where the upside-down glass trick comes in.
Placing a piece of paper or another suitable barrier over the drain and then placing a glass upside down over it creates an additional physical barrier. It can help keep insects away from the opening and reduce the chance that odors will enter directly through the drain.
However, the glass itself is not a magical plumbing solution, and covering every drain is not always necessary. The effectiveness of the method depends on the type of drain, the condition of the plumbing, and how long the home will remain empty.
There is also another reason people sometimes cover drains before leaving: insects.
Small flies and other pests can occasionally be associated with drains, especially where organic residue and moisture accumulate. Keeping a drain opening physically covered can make it more difficult for insects to move between the plumbing system and the room.
But there is an important distinction between preventing insects from entering through the drain and eliminating an existing infestation. If drain flies are already present, simply covering the opening will not necessarily solve the underlying problem.
Cleaning the drain and removing organic buildup can be more effective when dealing with recurring drain insects.
Before leaving for vacation, it is also a good idea to clean the sink thoroughly. Remove food particles, grease, and debris from the drain and surrounding area. This reduces odors and gives insects fewer sources of food.
The paper-and-glass method shown in the image is therefore better understood as an extra precaution rather than an essential rule that everyone must follow.
There is another important consideration: do not use an airtight covering as a substitute for maintaining the plumbing system. If a sink frequently produces sewer odors even when it is being used normally, there may be an issue with the trap, venting, drainage, or another part of the plumbing system.
In such cases, covering the drain only hides the symptom temporarily.
If you are going away for a short weekend, the water already present in a properly functioning P-trap will generally remain there. You may not need to perform any special procedure.
For longer vacations, particularly in hot weather, taking a few simple precautions can make sense. Run water briefly in rarely used drains before leaving, make sure the plumbing is functioning normally, clean kitchen drains, and consider covering drain openings if you are concerned about insects or odors.
Bathrooms should also be checked. Shower drains, bathtub drains, bathroom sinks, and utility sinks can all contain traps that may eventually lose water through evaporation.
If you have multiple drains that are rarely used, they may deserve attention before an extended absence.
Another useful step is to avoid leaving food scraps, dirty dishes, or standing water in the kitchen. These can contribute to unpleasant smells when the home is closed for several days.
The same principle applies to the garbage disposal, if your sink has one. Clean it according to the manufacturer’s instructions and avoid leaving food residue inside before leaving.
The upside-down glass in the photograph is therefore not really about the glass itself. It is being used as a simple temporary barrier.
The paper underneath helps cover the drain opening, while the glass keeps the paper in place and adds another layer between the drain and the room.
Some people may prefer a purpose-made drain stopper or plug instead. A properly fitting drain stopper can provide a more secure barrier than a loose piece of paper and glass.
If you decide to use a temporary covering, make sure it does not create a safety problem or interfere with the sink in a way that could cause water to overflow.
Ultimately, the most important protection is the plumbing trap itself. The small amount of water sitting inside the curved pipe beneath the sink is what normally prevents sewer gases from entering your home.
The glass trick is simply an additional precaution that may help while the home is unoccupied.
So if you see someone covering their sink with paper and placing a glass upside down before vacation, they are not necessarily doing something strange. They are using a simple household trick intended to keep the drain covered and reduce the possibility of odors or insects coming through the opening while the home is empty.
It is a small step, but combined with cleaning the kitchen, checking drains, removing food waste, and making sure the plumbing is functioning properly, it can help you return from vacation to a fresher and cleaner home.
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