Toilet siphons: description and rules of use

The reliable operation of a toilet bowl in an apartment or a private house depends on all its devices, as well as on the correct installation of this plumbing equipment. The most important part of any toilet is siphon unit, through which the flushing water flows into the sewer pipe. We will describe this whole unit in more detail, since it is present in the toilet bowls of all models without exception – both outdated and ultra-modern.


In addition to the function of a conductor of discharges from the toilet bowl into the sewer system, the siphon acts as water seal, preventing the penetration of corrosive gases from the sewer into the home. In any apartment, you can count at least 4 siphon devices installed on plumbing equipment:

  1. on the flush from the toilet;
  2. under the kitchen sink;
  3. under the sink in the bathroom;
  4. on the drain from the bathroom bowl.

However, the toilet siphon unit has its own peculiarity, distinguishing him from others. The fact is that the hydraulic siphon valve for the toilet bowl, which is a part of the outlet pipe bent in the form of the Latin letter “U”, is cast together with the bowl. That is, the water seal of this sanitary ware is already built in during manufacture at the factory and is an integral part of it. The same element on the drain from the sink or bathroom is mounted with his own hand when installing plumbing.

Often it is the U-shaped part of the outlet pipe, in which a hydraulic seal is formed, which prevents the penetration of gases and odors from the sewer pipes into the apartment, is called a siphon.. But on this issue, the opinions of experts differ. From the technical point of view, it would be more competent to call the entire outlet pipe a siphon, moreover, together with a collar and other fitting, which may be needed to connect the outlet to the sewer pipe.

All this can be explained by the fact that the operation of the siphon completely depends not only on the strength of the flushing water, but also on the resulting negative pressure after the hydraulic seal when the liquid is discharged into the empty sewage line..


The toilet siphon unit consists of the mentioned U-shaped outlet configuration and his inlet and outlet horizontal parts, and elements of connection of the outlet with the sewer pipe. Most often, the connection of the tail of the outlet pipe with the sewer pipe is performed with a plumbing cuff, which has either a rigid structure in case of coincidence of the mating pipes along the axes, or using a corrugated connection with slight deviations of the pipe axes. If there is a significant mismatch in the placement of the toilet bowl and the sewer pipe, you have to install the outlet using additional elements in the form of curved or straight sections of sewer pipes (or fitting).

A water seal in the U-shaped section of the outlet pipe is formed due to the difference in height of the channel leading to this section and the tail of the pipe. The height of the last element is much higher, therefore, the flushing water remaining in the bend of the U-shaped section of the outlet channel is not able to overcome such a difference even under the influence of the pulling force from the sewer side.

As a result, a water blockage is formed at the bend point, blocking the entire lumen of the toilet bowl outlet. The path of gases from the sewer to the bathroom of the dwelling is securely closed.


Since we will consider the outlet pipe as a siphon for a floor-standing toilet, with a bend of the water seal inseparable from it, depending on the type of outlet, there are also several types of siphon construction.

  1. Horizontal outlet. This group of toilets is divided into two types: with oblique and direct release. The shank of the outlet pipe in the first case is parallel to the floor, in the second case – at a slight angle.
  2. With vertical release. In this embodiment, the tail piece of the outlet pipe protrudes vertically downward. Toilets with such a design are found in our country only in private housing construction. In apartment buildings, this method of release is not used due to the complexity of installing the sewerage system..
  3. With the release of “vario”. A universal solution for complex cases of connecting toilets to the sewer. It is another type of horizontal outlet, but with the difference that the tail pipe of such a toilet bowl is shortened. This allows you to attach it to the sewer by sliding it close to the wall.


In the bulk of floor-standing toilets, the predominant popularity among the population is horizontal outlet models. And of their main varieties – with oblique pipe. This is explained, first of all, by a simpler combination with the sewage system of this variant of the outlet pipe. In addition, the water will not stand from the nozzle to the sewer pipe, unlike the models with direct discharge. This means that the likelihood of leaks in this place is minimized.

In cases of installing toilets with direct discharge, most often problems arise precisely because water flows in the joints of the horizontal section from the toilet to the sewer line, since water always remains there.

The choice of a siphon (read – “outlet”) is also influenced by the size of the toilet room. If you have to save literally centimeters so that you can create the necessary conveniences both for using the toilet and in order to repair it in case of malfunctions or adjust, then you can purchase a toilet with the release of “vario”.

For your own house, which is planned for construction, you can use version with vertical outlet. He has Benefits: uses water sparingly, and the bowl flush is much better than for models with other types of release. In addition, the sewage system runs under the floor slabs, so the noise from the operation of the flush system will practically not be heard..

Operating rules

In order for the siphon to work reliably, and to flush out efficiently, a good pressure of water from the drain tank is required.

But completely different toilet systems are responsible for this – water filling and drain.

      As for the siphon unit in the toilet bowl, the following rules for its operation can be noted.

      1. Do not hit in the area of ​​the exhaust pipe with metal or other solid objects (this happens when the apartment is being renovated). It will not work to replace the broken pipe – the bowl is made entirely with all devices made of fragile materials – faience and porcelain, which absolutely cannot withstand mechanical shock.
      2. A strong fastening of the toilet bowl is required when installing it. When using the equipment and caring for it, do not allow the bowl to swing – this will lead to its displacement and possible depressurization of the siphon joints. As a result, it will be necessary to seal the joints with a sealant or replace the sealing rings on the cuff..
      3. In the case of ineffective operation of the siphon or flush in general, the reason sometimes lies in the clogging of the outlet channel or water seal with debris and deposits. In this case, you should try to clean the part of the channel to the water seal with a flexible brush, and then flush the entire system with special agents designed to clean sanitary ware made of the appropriate material from deposits and other blockages..

      See tips for proper toilet installation.

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