Sink drain - you should know about it

Of course, if you install a new washbasin, you must also properly assemble the drain. How this process is in the first place, what parts it consists of, and how to properly assemble it, you will read in this article. In addition, how to get him in the constipation case best again.

Important parts with standard connections

For standard connected sinks you will find the following parts in the sequence, in order from top to bottom:

  • drain valve
  • mold ring
  • Valve body
  • dip tube
  • siphon
  • Connecting piece to the sewer pipe

The first three parts (drain valve cup, mold ring and valve body) are also called "inlet fittings".

The drain in this form is only used for sinks. For kitchen sinks, a number of additional parts are added, and the drainage of bathtubs and shower trays also contains different parts.

inlet valve

In the inlet fitting is only the drain valve (in modern sink in conjunction with a so-called spout closure) in the basin. Form ring and valve body are below the wash basin.

A closure with rubber stoppers, such as those found in stainless steel sinks, is no longer common in sinks today. Instead, a so-called spout is used. It is usually operated via a lever mechanism that raises or lowers the closure.

When lowered, no water can drain and the basin is filled. When the lever is operated in the opposite direction, the stopper rises and the water can run underneath. This also provides some protection against flushing larger objects into the drain, which could then clog the drain.

dip tube

The so-called dip tube connects the valve body with the siphon. The length of the dip tube is important to get the right height to the drain connection. When measuring, you should therefore be very accurate, and try to piece together all parts to determine the correct length.

Cut tubes correctly

If the required length is correctly marked, the drainage pipes (often available as complete system with siphon) can be sawn off with a metal saw. Due to its fine toothing, the hacksaw is best for sawing HT pipes (temperature resistant even for higher temperatures and standard drains).

Thereafter, the resulting burr must be removed carefully with a knife or cutter. The cut edge should then additionally be chamfered with a file.


The siphon is an odor trap that prevents malodors from rising out of the drain or sewers and entering the room through the drain valve.

Usually, a siphon consists simply of a curved piece of pipe, which is installed between the dip tube and fitting to the sewer. Such a siphon is also called tube siphon.

If less space is available, a so-called bottle siphon can also be installed. Such siphons are also used (and above all) for very low, often flush-mounted shower trays use. In contrast, baffle closures and bell trap closures are generally very rare.

Check the siphon regularly

Siphons are one of the main places where clogs form in the drain. At the bottom of the siphon, settled substances accumulate which, over time, form a viscous, malodorous sludge.

Removing this regularly, this is a very good prevention against constipation. Even things that were accidentally washed into the sink, you will find very often in the siphon mud again.

Connections on the siphon

The siphon is connected to the dip tube and the connection piece to the sewer pipe. Here, a simple ring seal is used. The pipes leading to and from the siphon are inserted into the siphon and the seal is located at the end of the pipe. This compound is also called crimp connection.
Thereafter, the connection is secured with a union nut, which is screwed onto the thread of the Siphonstücks. In order for the pipes to slide more easily into the siphon pieces, a suitable lubricant should be used.

Pipes must never be inserted into the fittings as far as the stop. There is still a so-called expansion compensation must be maintained (around 10 mm). You should always pay attention to this during installation, as well as the tightest possible screw connection of the union nuts.

Connecting piece to the sewer pipe

The connection piece to the water pipe can also be designed as a movable hose. This usually makes it easier to adjust the connection.

In any case, make sure that the connection part protrudes sufficiently far into the water pipe and that it is not too short. The tube can be cut to length in the same way as the dip tube. Also pay attention to any deviating pipe diameters and, if necessary, use suitable connecting pieces and adapters.

Laying drains free

It is best to always use mechanical methods first in case of blockage. Recommended is a pipe spiral, alternatively, you can try it first with a suction cup ("Pümpel").

On drain cleaner, especially on inorganic means (as granules or liquid) you should avoid as possible because of their dangerousness and their ecological concern. Other means of cleaning the drain can also be found in this article.

Tips & Tricks

Clean your siphon regularly by simply removing it and rinsing it thoroughly. To avoid bad smells, if you do not use a drain for a long time (eg on vacation) simply drip some glycerin or cooking oil into the drain.

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