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Laying sewage pipes: How the professional does it

Laying sewage pipes: How the professional does it

Laying sewage pipes: How the professional does it

Sewage pipes are usually laid by a specialist. However, experienced do-it-yourself enthusiasts can also tackle the problem themselves – this also applies to repairs and additional connections. Modern plug-in systems make work much easier – but it doesn’t work without technical terms and basic rules.

There are often sewage pipes in houses and flats: shower, washbasin, WC, washing machine, dishwasher, sink, bathtub and condensing boiler need a drain, often also the floors of bath, sauna or laundry room, but in different sizes. An overview of the most important abbreviations and designations as well as some installation tips.

Sewer pipes: The most important components and types

Wastewater pipes can basically be distinguished according to the following criteria:

Nominal diameter

The industry produces wastewater pipes for standard requirements with diameters from 32 to 160 mm. However, the standard sizes for do-it-yourselfers are manageable:

Wash basin, dishwasher, washing machine: DN = 40 – 50 mm

Showers, bathtubs: DN = 50 – 75 mm

Toilets: DN = 100 mm

sewer pipes, graphic: sewer pipes, graphic: sewer pipes, graphic:

The abbreviation DN (French: diam├Ętre nominal, English: diameter nominal) denotes the nominal diameter of a pipe. This refers to the inside diameter.


The grey house drainage pipes traded in DIY stores are made of polypropylene (PP for short). They are also known as HT pipes. This means that they are suitable for high temperatures, i.e. hot water. According to the standard, HT pipes should also be resistant to aggressive waste water and flame-retardant.


The do-it-yourselfer has standardised drain pipes at his disposal throughout. This makes it possible to combine parts from different manufacturers. In Germany the products mostly come from the companies Marley or Ostendorf. There are rough quantities of fittings, but the do-it-yourselfer usually needs them:

  • Straight pipe
  • Traded in lengths of 25, 50, 100 and 200 cm, with or without printed length scale
  • bows
  • with angles of inclination of 15, 30, 45, 67 and 87 degrees (sometimes also called knees)
  • Straight sewage pipe with printed length scale.

There are essentially three versions:

  • Single branch
  • Triple branch; it brings together three lines (top, right, left), all on the same level.
  • Corner branch; also joins three lines that lie above the corner).
  • Socket

Also known as a sliding sleeve; the technical term refers to nothing other than a pipe connector. It has a sealing rubber at both ends and connects two pipes, which then lie inside. At its counterpart, the nipple, the pipes to be connected are placed on the outside.

Installation in the wall or floor

Wherever possible, do-it-yourselfers in the bathroom and kitchen will want to hide the not particularly attractive HT pipes. If a renovation is pending anyway, this is usually not a problem, because the pipes are plastered or covered with new tiles.

  1. The first step is to check whether the walls in question can accommodate the necessary pipes. Light partition walls only twelve cm thick and load-bearing walls are not suitable or only partially suitable. In case of doubt, do-it-yourselfers should consult a structural engineer before starting.
  2. Then it is recommended to mark the desired course of the pipes with two parallel lines on the wall. For a pipe with DN 40, a slot of at least 50 mm width must be provided. All recesses should be inclined, i.e. never completely horizontal, so that the pipes can later be laid with an optimum gradient of two percent. This means that a pipe one metre long is inclined by two centimetres; the inevitable minimum inclination is one centimetre – otherwise the waste water cannot drain off.
  3. The drawing shows which pipe lengths, bends and branches are required. Anyone who does this work for the first time should buy the material and put it together provisionally. This makes it easy to check whether the planned pipe routing can be achieved. Inexperienced do-it-yourselfers should better buy different bows in order to be able to vary. Excess (and unused) material can usually be returned to the large DIY stores within four weeks if the receipt is presented.
  4. Walls made of aerated concrete are the easiest to work on. But a concrete wall can also be cut with a grinder or a hand-held circular saw with a diamond disc. Once the slots have been sawn, the centre pieces are knocked out with a percussion drill or by hand with a hammer and chisel. Then the pipes are mounted in the wall.
  5. The pipe slots are only closed after a rinsing test, i.e. a tightness test. Gypsum or lime-cement plasters, which are available as a ready mix in 25 kg bags for six to eight euros, are suitable for this purpose.

Installation on the walls

The installation of sewage pipes in front of the wall is very easy. All you have to do is buy enough additional fastening clamps and drill holes in the walls. Dowels are placed there to screw in the clamps (with or without sound-absorbing rubber insert).

In the case of short distances, do-it-yourselfers can often make the pipes disappear optically by placing sheeting of plaster, fibre cement or wood in front of them.

Laying rules and tips

Whether in the wall or outside – these tips will help do-it-yourselfers to lay the sewage pipes more easily.

Cutting pipes

It is advisable to use a saw with fine teeth, such as a hacksaw; the tough PP tube will then not fray as much at the cutting edge. Deburring is still necessary: inside with a sharp knife, outside with a fine file.


Pipes and connectors are never inserted into each other as far as they will go in order to absorb their expansion when heated. Tip: Push the pipe into the bend until it touches – apply a pencil stroke to the pipe at the transition point – pull the pipe out again until the stroke is at least 1 cm away – done.

Place clamps

So that vertically running sewage pipes do not sink due to their weight, the clamps are fastened just behind the bead in which the rubber seal lies. The maximum distance between the clamps for vertical pipes is two metres; if the pipe is cut into pieces, a clamp should be placed under each bead. Of course, it is safer to fasten the down pipes at a distance of one meter.

Horizontal pipes should always be fastened at the transition points, i.e. in front of and behind a sleeve or bend, so that they always keep their gradient and also tolerate an occasional jostling. For long, straight stretches, the distance between the clamps is a rule of thumb: The distance corresponds to ten times the pipe diameter. DN 50 pipes therefore receive a clamp approximately every 50 cm.

Forming angles

For all waste water pipes, the principle of breaking the water flowing away as little as possible applies. There is a good reason for this: when wastewater is slowed down, particles that are easily carried along are deposited, which leads to permanent blockages. This ensures smooth running and avoids unnecessary impact points. For this reason, no 90 degree angles are used for corners, but two 45 degree arcs are laid so that the water does not have to take an abrupt turn.

Use lubricant

Assembly can be made easier by applying a friction-reducing paste to the pipe ends before they are plugged together. Such lubricants are available, for example, in tubes of 250 g and cost from four euros. The paste protects the rubber seal, because during installation the fittings are usually removed or turned several times until they fit properly.

Setting transitions

Waste water systems are designed in such a way that the respective collecting pipes always have a larger diameter than their individual inlets. For example, the pipes from the shower, bathtub and washbasin run into the collection pipe of a bathroom. For example, there may be a DN 75 or even DN 100 collecting pipe, but only a DN 40 pipe is required for the additional sink. So that the transition is carried out professionally, so-called reducers are used. In this way, any conventional line can be routed to the next larger one, e.g. DN 40 to DN 50.

Professional breakthroughs

Sometimes it is unavoidable to run the new sewage pipe through a wall or the floor. In the case of wooden beam ceilings, care must be taken not to hit a load-bearing beam when piercing; in the case of concrete ceilings, the steel reinforcement should not be damaged under any circumstances. In a suitable place, a circular breakthrough can be made in the wall or floor with the aid of a drill bit. It must be large enough so that a larger piece of pipe can be inserted and fastened with mortar or plaster. The sewage pipe then runs through this lining, which must have a clearance of at least five mm and must not be concreted in.

Think about maintenance

Even professionally installed sewage pipes are not always protected against deposits, calcification or blockage. It is therefore useful if the pipe is provided with a cleaning pipe at an easily accessible point. This is nothing more than a branch with a removable cover. The installation site should be located before the junction into the next larger pipe and as far away as possible from the feed (the drain of shower, washbasin, tub and so on). In an emergency, a cleaning spiral can be inserted into the lockable access.

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