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Odor trap: How a siphon protects you from sewer odors

Even in the cosiest bathroom, nobody would stay long if there were no odor traps. These devices are installed between the sewer connection and the drain of all sinks, sinks, showers, toilets and bathtubs, preventing the sewer smell in bathrooms and kitchens.

Everything at a glance:

  • Odor traps, including siphons, ensure that there is no odor of sewer in buildings.
  • They are installed between the sewer connection and sanitary facilities such as sinks, showers and bathtubs.
  • Toilets also need siphons. However, these are already permanently installed in the toilet bowl.
  • The classic among odor traps is the U-shaped pipe siphon. Bottle or cup siphons, on the other hand, are a modern variant.
  • There are odor traps made of both plastic and metal. The latter are usually coated with chrome.
  • The cheapest models start from 10 euros. Expensive, high-quality products can be priced up to the 200 euro mark.


Odor traps are inconspicuous components between sanitary facilities such as wash basins, sinks or showers and the sewer pipe. They ensure that there is no muffling in buildings despite the direct connection to the sewer system.

What is an odor trap?

An odor trap is a device in front of the sewer connection. It prevents unpleasant odors and smells from entering the building through the drain from the shower, wash basin and toilet. An odor trap is designed in such a way that liquids can pass through, while gases and bad smells remain in the pipe to the sewer.

A common name for the Odor trap is also siphonwhich means something like siphon or riser pipe in French. Seldom odor traps are also called trap, which comes from English and stands for odor trap.

The most commonly used odor traps are:

  • Pipe odor trap (= pipe odor trap)
  • Bottle odor trap (= cup odor trap)

Bell odor traps are also used less frequently.

Siphons are made of plastic or metal. Brass coated with chrome is used particularly often. So that the chrome layer lasts for a long time, rust does not form and leaks arise as a result, you should avoid using harsh cleaners in the drain pipe as far as possible.

Where do you need an odor trap?

A siphon is necessary wherever wastewater flows into the sewer system. In the house, you need a siphon on toilets, urinals, showers, bathtubs, wash basins, sinks and bidets.

In toilets, such odor traps are already permanently installed in the toilet bowl; in all other sanitary facilities, they have to be installed individually between the drain and the sewer pipe.

Odor traps are not only necessary in the house, but also outside in courtyard entrances, in the garden or near gullies in the street - wherever there is an opening to the sewer.

How does an odor trap work?

Even if there are different types of siphons for all possible areas of application, they work according to the same principle: the rise of gases and stench from the sewer is prevented by a water stop.

If waste water, for example from the sink or shower, runs through the drain pipe, not all of it disappears into the sewer. A small amount water always remains in the odor trap and forms a Barrier between sewer pipe and drain pipe. Gases and odors cannot spread through liquids and remain in the sewer pipe. The fact that the shower, sink and toilet are used regularly ensures that the water remaining in the siphon is constantly renewed.

If it is not used for a long time, however, the water in the odor trap can partially evaporate, the barrier is no longer completely in place and bad smells can escape from the sewer.

So that the siphon does not dry out and the apartment smells like sewage when you are away for a long period of time, pour a small amount of cooking oil down the drains.

What should you pay attention to when buying?

When buying a siphon, pay attention to the horizontal and the vertical distance between water drain and sewer pipe. In the case of wash basins, this is usually uncomplicated, as odor traps can be set and adjusted up to a certain point. There is also a very large selection here, so that there are solutions for almost every washbasin.

It gets a little more demanding with modern construction methods such as floor-level showers. Because there is no shower tray here, there is no space under the shower floor necessary for the siphon. If the sewer connection is then not deep enough, the gradient between the water drain and the sewer may not be sufficient for trouble-free drainage. For such special cases there are now also very space-saving odor traps.

If you don't have the technical know-how here, you should definitely contact a plumbing company. Even if you can find a siphon that connects to your water drain and sewer pipe - if the slope is too small, you will run into problems with water not draining.

Odor traps: There are these variants

Siphons are permeable to liquids, but they hold back gases and smells in the sewer pipe. A small amount of water remains in the siphon after each flush and serves as a water stop. There are different shapes depending on the area of ​​application.

What is a pipe odor trap?

The pipe odor trap, or pipe odor trap, is the simplest form of a siphon and the most frequently used type of siphon under wash basins. It is still found as standard in older bathrooms in particular, but in new buildings and refurbished bathrooms it is increasingly being replaced by more modern, visually appealing types of siphons.

The tube siphon has a at its deepest point U-shaped or S-shaped tubein which some water always remains automatically. This so-called sealing water must be so high that the bend is completely filled and no gases and smells can rise from the sewer pipe through the drainage pipe.

In pipe siphons, the waste water is flushed through with strong pressure, which is why dirt particles and other solids rarely get stuck and the siphon is usually always free. Experts therefore speak of a self-cleaning effect.


  • hardly any deposits
  • rarely constipation
  • self cleaning
  • cheap (metal: from 8 euros)


  • bulky
  • cumbersome dismantling
  • outdated design
The fill level of the sealing water in the siphon is standardized. DIN 1986-100 states that this height must be 50 millimeters for waste water drains and 100 millimeters for rainwater drains.

What is a bottle odor trap?

The bottle odor trap does not have a U-shape or S-shape like the classic tube siphon, but one bottle-like containerin which the sealing water collects. Depending on the design, this container can also be shorter and look more like a cup than a bottle. This is why the bottle siphon is also called a cup siphon. The functional principle remains the same. Due to its modern design, it is increasingly replacing pipe siphons under wash basins.

With this siphon variant, the vertically sloping drain pipe from the wash basin or shower ends in a bottle or cup-shaped vessel. Rising water in this container overflows at the edge of the cup and from there into the canal. The drain pipe itself always ends below the sealing water surface in the vessel.

Bottle or cup siphons have a comparatively small installation depth and only require a few centimeters of space below. However, they are also more prone to deposits and soiling than pipe siphons, as the flushing effect does not occur. However, cleaning the siphon is quick and easy.


  • modern design
  • space saving
  • easy to clean


  • not self-cleaning
  • tends to clog
  • slightly more expensive than pipe siphons (metal: from 10 euros)

What is a bell trap?

The bell siphon also owes its name to its shape. There is a Everted container over the sewer drain pipe, similar to a bell. The container has openings at the bottom through which water can penetrate. As soon as the water inside rises, an additional device creates a strong negative pressure at a certain point. The wastewater is then literally sucked into the sewer pipe. The negative pressure remains until all the wastewater in the sewer has disappeared.

Bell siphons are mainly used in aquariums and play a subordinate role in the sanitary area. However, this siphon variant can also be found as floor drains in shower areas.


Traps are important so that there is no smell of sewer in buildings. Because every waste water, whether from the shower, wash basin, sink or toilet, when it disappears in the drain, runs directly into the sewer system. The odor trap, also known as the siphon, is located between the drain and the sewer connection. Liquids can pass through it, but gases and odors are held back by a water barrier in the sewer pipe.

There are many different siphons depending on the space required, area of ​​application and design. Most often, pipe odor traps and bottle or cup odor traps are installed. While the former is still often to be found in old bathrooms as a classic siphon construction, modern, chrome-plated bottle siphons are more likely to appear in new buildings and refurbished bathrooms. In terms of costs, there are no longer any great price differences. Cheap metal siphons are available from around 10 euros. Plastic products are a little cheaper. High-quality models cost between 50 and 70 euros. However, if you want exclusive variants, you can also spend just under 200 euros on a siphon.