A leaky siphon is annoying! How it came to be, plays mostly no more role with the repair. Because it is much more important to get the siphon tight again. But how? With the bottle siphon, often only the downpipe has to be replaced. But sometimes it is better to replace the old siphon completely. And then you have to “mount the new siphon”! But don’t worry – we’ll show you how easy it is in the following instructions.


In order to mount a new siphon, not much tools are usually required. In most cases, a measuring tape, a pipe wrench, a mitre box and a hacksaw are sufficient.

In addition to the new siphon, only a little abrasive paper is needed to deburr the cut pipes. In addition, a cloth should be available to wipe away any leaking water and another dry cloth to check for leaks. Read more about plumber tips for greater details.


Before the new siphon can be installed, the old siphon usually has to be removed first. To do this, first loosen the upper union nut on the drain valve. If this nut is too tight, a pipe wrench will help.

Tip: These threads are usually normal right-hand threads. The nut is therefore loosened by turning it to the left.

Once the nut has been loosened, it can be unscrewed by hand. Removing the old siphon is then child’s play. Because the siphon only has to be pulled out of the drain. Just turn and pull once and the siphon is removed! If the sleeve seal remains on the pipe, it is removed and put back into the drain.

Attention: There is still a lot of water in the siphon! So don’t tip it and empty it in another sink first.


If you are curious and want to know why the old siphon leaked, you can take a closer look at it. To do this, the old siphon is simply dismantled completely. It starts with the union nut on the odour seal. This is loosened and then unscrewed. Then the downpipe can be pulled out of the trap.

At the downpipe there is a plastic pipe, which is put over the metal pipe. If this is pulled off, the cause can already be seen: A lot of deposits can be seen on the metal pipe. These make a tight connection of these two pipes impossible. Therefore the water overflowed exactly at this point. The cause would be found in this case.


In order to install the new siphon, its height and depth must first be adapted to the local conditions. The height can be easily removed.

The siphon is screwed to the drain valve and the missing distance is inspected. The height of the siphon can then be adjusted using a measuring tape or eye gauge. To do this, the second union nut is opened near the odour trap. Since also with this model a plastic pipe is put over the metal pipe, the plastic pipe must be shifted simply only in the height. Then the pipe can be pushed back into the trap and fixed with the union nut. A new check of the height follows.

If the height of the siphon fits, the depth of the horizontal drain pipe can now also be measured. To do this, determine the following lengths: the depth at which the drain pipe penetrates the socket seal (here 2 cm), the distance from the socket to the siphon (here 3.5 cm) and the depth at which the drain pipe penetrates the siphon (here 2.5 cm). The total length of the horizontal pipe in this project must therefore be 8 cm.


It’s almost done, because next the new siphon can be mounted. To do this, the pipe that has just been cut to length is inserted into the sleeve seal in the drain pipe of the wall. The cut-off side is inserted into the sleeve seal. The beautiful, uncut side, on the other hand, points in the direction of the siphon. Then the screen can also be pushed over the pipe so that the tile cut-out disappears behind it.

Then the siphon, or rather the odour trap, is put over the newly installed drain pipe.

Note: This is not the case with every model. This is because a squeeze seal is often used here!

Finally, only the flat gasket has to be inserted or checked into the upper union nut. This can then also be hand-tightened with the drain valve. And already it is done: The siphon is mounted! But whether the siphon assembly was really successful can only be shown by a subsequent function test.


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