# What Exactly Is a Trap and Why Is Trapping Necessary?
A trap is one of the most important components of any drainage system. Many people believe its purpose is simply to allow water to flow into the sewer, but in reality this is possible even without a trap. The primary function of a trap is to prevent sewer gases and unpleasant odors from flowing back through the drainage pipe into the building. Without a properly installed trap, even the best-installed linear drain, washbasin, or floor drain can become a source of unpleasant smells.
In practice, a floor drain trap can be made quite easily, not only by using ready-made components but also by building one yourself with properly connected drainage elbows. This solution is often used in garages, workshops, linear drainage systems, and utility rooms.
The operating principle is very simple. It is a wet trap – water remains in a specially shaped section of the pipe, creating what is known as a water seal, usually described as a U-shaped trap. This water seal is what prevents sewer gases from flowing back into the room.
When building a trap from pipe elbows, two 45° or 90° drainage elbows are typically used to create a characteristic low section in the pipe. After water passes through, a small amount remains in this depression, forming an odor barrier, as shown in the image below.
A trap made from pipe elbows is especially popular where a standard trap would be difficult to install or would take up too much space. It can be used, for example, in garages, where standard traps integrated into drainage systems may dry out over time and stop working. In certain situations, it is actually a better solution than traditional prefabricated traps.
A pipe elbow trap has several advantages – it is simple, inexpensive, quick to make, and perhaps its greatest advantage in some applications is that the water in a properly designed elbow trap will not evaporate.
The most commonly used components are standard PVC drainage elbows with a diameter of DN50 or DN75, depending on the installation. For most residential applications, DN50 is sufficient, as it is the most common size used for linear drains and garage drainage systems.
A simple trap can be made using:
In practice, smoother transitions generally perform better because they reduce the risk of debris buildup and improve water flow. However, this is not always essential, as most modern drainage systems are equipped with sediment traps that prevent debris from entering the drainage pipe.
To build your own pipe elbow trap correctly, the most important step is to create a proper low point in the drainage pipe. The installation should form a U-shaped profile or a gentle "wave". There is no need to create a very deep trap—a shallow depression is sufficient as long as it permanently retains water.
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When installing a pipe elbow trap, remember to:
For garage drainage systems, the trap is often installed directly on the drainage pipe beneath the concrete floor. This allows for high drainage capacity while effectively preventing unpleasant sewer odors from entering the garage.
This is a very important consideration. In most cases, cleaning this type of trap is not necessary because strainers and sediment traps used in drainage systems prevent debris from entering the pipe. Industrial drainage systems are not always equipped with built-in traps, but they generally include effective sediment collectors.
Despite this, many people believe it is worth ensuring that the trap remains accessible for maintenance. A good solution is to install the trap on a section of pipe located slightly away from the main traffic area, allowing for the construction of an access chamber—a space that is not filled with concrete and provides emergency access to the trap. This chamber should be fitted with a suitable cover, but it should not be located where it will be subjected to heavy loads, especially vehicle traffic (if installed in a garage). Therefore, the location of the chamber containing the trap should be carefully planned. Fortunately, this is not an expensive solution.
One of the most common mistakes is creating a trap that is too shallow or an almost completely straight drainage pipe. In such cases, water cannot remain inside the system, allowing sewer odors to freely enter the building.
Another common mistake is using too many sharp elbows. This can reduce water flow and increase the risk of clogging. An insufficient pipe slope is also a frequent issue, causing water to stagnate inside the drainage system.
Yes—it is one of the most commonly used solutions for garage drainage systems and linear drains installed in workshops and utility rooms. Traditional traps often restrict drainage capacity, dry out over time, or make installation within a concrete floor more difficult.
A trap made from pipe elbows is simple, inexpensive, and highly durable. It can also be easily adapted to the specific layout of the drainage installation. In garages, it offers the additional benefit of handling larger volumes of water and debris carried in by vehicles.
If you have basic knowledge of drainage installations—and at least some experience in making watertight pipe connections—the answer is definitely yes. Building a trap from pipe elbows is not difficult, yet it effectively protects your drain from unpleasant sewer odors.
The key is maintaining the correct pipe configuration and creating a section where water can remain permanently. A properly constructed trap can operate reliably for many years, whether it is installed in a garage, bathroom, workshop, or industrial facility.
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