Step-by-step installation of HT waste pipe

We are still preparing products.

But you can look at other categories.

Installation of HT waste pipe step by step: complete practical guide

The installation of waste pipes made of HT material is one of those installation tasks that at first glance seems simple – plastic pipes, rubber seals, a few elbows – and yet it is precisely here that most of the problems arise, which later trouble homeowners and even experienced plumbers. A wrong slope, a forgotten inspection fitting, too many elbows in a row without ventilation, an unsuitable diameter – all of these are mistakes that can go unnoticed for years until suddenly they don't. In this article, we will thoroughly examine the installation of the HT waste system step by step, with an emphasis on the details that determine whether the installation will work for decades or become a source of endless worries.

If you are still planning which system to choose, read the topics HT versus KG system: which waste system to choose and why and How to choose the right HT pipes and fittings for the waste system. These articles will help you before purchasing the materials.

What is the HT system and why it is used for internal waste pipes

HT (from the German "Hochtemperatur") is a system of plastic pipes and fittings made of polypropylene material (PP), designed for internal gravity drainage. Unlike the KG system (used for external, underground sewage), HT is optimized for interior conditions: higher temperature fluctuations of waste water (up to 95 °C short-term), lower mechanical load from external forces, and smooth inner walls that minimize sedimentation.

The PP material is more resistant to aggressive cleaning agents, fats, and weak acids than older materials such as cast iron or PVC. At the same time, it is relatively quiet compared to metal systems, although the noise level also depends on the mounting method and insulation measures. The connection of pipes and fittings is made via a rubber seal placed in the neck – so no gluing, no open flame, no special tools.

The connection principle of the HT system is simple and reliable: the neck of the fitting contains a groove into which a ring-shaped rubber seal is inserted. The pipe or the smooth end of another fitting is inserted into the neck. The seal is compressed and creates a watertight connection that also allows for linear expansion – which is very important with hot waste water.

Before installation: what you need to prepare and plan

Project preparation and dimensional plan

The most common mistake we encounter in practice is "improvised" installation without any schematic plan. The plumber buys the material by eye, on the site he finds out that he is missing one elbow, he has to go to the warehouse, in the meantime the concrete is poured without a transition piece... You can avoid this by drawing a simple axonometric scheme of the entire waste pipe route before purchasing the material.

Mark the following in the scheme:

position of each device (toilet, sink, bathtub, shower, kitchen sink, washing machine)
diameters of individual sections – usually DN110 for a toilet, DN50 or DN75 for a sink and shower, DN50 for a kitchen sink
places where a change of direction (elbows), branching (branches), or diameter change (reductions) is needed
position of cleaning fittings – at least one on each vertical rising pipe, ideally also on long horizontal sections
height of the connection to the horizontal collector pipe or sewer inlet

If you are unsure about the correct diameters for individual devices, the topic What HT pipe diameters do I need for a toilet, sink, and shower will help you. The correct diameter is not only a matter of standard – diameters that are larger than necessary paradoxically cause faster clogging, because the flow speed of water decreases and solid substances settle.

Required tools and accessories

Plastic pipe saw or circular saw with fine teeth (not a hand saw – the cut would not be straight)
File or scraper for deburring the cut
Water level (at least 60 cm, ideally 120 cm)
Tape measure (flexible metric tape)
Pencil or marker for marking the insertion depth
Vaseline or special mounting paste for seals (never oil-based products!)
Clamps and anchoring materials corresponding to the pipe diameter
Drill with appropriate bits and core bits for penetrations
Hose clamps or self-tapping screws for fixing clamps

Step 1: Measuring, cutting, and preparing the pipes

Correctly measuring the length of the HT pipe section is fundamental. A seemingly trivial task, but in practice, it happens that the installer forgets to subtract the insertion depth – that is, the part of the pipe that physically inserts into the neck of the fitting or into the neck of the adjacent pipe. The insertion depth depends on the diameter:

Diameter DN	Insertion depth (mm)	Minimum pipe length for connection
DN 32	45 mm	90 mm
DN 40	48 mm	95 mm
DN 50	52 mm	105 mm
DN 75	60 mm	120 mm
DN 110	68 mm	140 mm

After measuring and marking the cut line, draw it perpendicular to the pipe axis. The cut must be truly perpendicular – a slanted cut will cause the seal to be unevenly loaded and the connection will be leaky. After cutting, use a file or scraper to remove internal and external burrs. Internal burrs catch waste and create a point of retention for dirt; external burrs damage the rubber seal during insertion.

On the smooth end of the pipe, draw a line with a pencil or marker at a distance equal to the insertion depth. This line will show you during installation how far you have correctly inserted the pipe.

Step 2: Preparation of connections and sealing

Check the rubber gasket supplied in the socket – it must sit evenly in the groove all around the circumference, must not be popped out or turned upside down. Before inserting, apply a thin layer of vaseline or mounting paste to the smooth end of the pipe (not on the gasket!). The aim is to reduce friction during insertion, not to lubricate the gasket itself.

Never use motor oil, WD-40 or other oil-based products – these cause degradation of the rubber gasket and over time will lead to leakage. Vaseline (technical petroleum jelly) is the standard in this context; some manufacturers supply a special mounting paste that is compatible with PP.

During the actual insertion, move the pipe evenly, without swaying movements. Insert the pipe straight along the axis, not at an angle – an angled insertion can dislodge the gasket from the groove. When you feel resistance from the gasket, push a little further until the marker line on the pipe aligns with the edge of the socket. This means the pipe is inserted to the stop.

Important detail: after inserting to the stop, pull the pipe back by 10 mm. This creates an expansion gap, which allows for thermal expansion of the PP material. The pipe heats up and elongates when hot wastewater flows through it; without this gap, it could lead to deformation or loosening of the connection.

Step 3: Installation of the vertical rising pipe

The vertical rising pipe (technically referred to as a "riser") is the backbone of the building's drainage system. In single-family homes, it typically runs from the foundation slab to the roof, where it is terminated with a vent pipe. In apartment buildings, it is shared by multiple units.

Installation of the riser starts from the bottom up. The first section is usually a transition from the horizontal drainage pipe (KG system in the foundation slab) to the HT system, implemented using a transition fitting or HT reducer if the diameters change. This connection must be accessible – either in a technical room or behind a maintenance hatch.

Rules for the riser:

Secure the riser with fixed clamps ("fixed point" – so-called "fix-point") at intervals of maximum 10 x DN, i.e., every 1.1 m for DN110. The fixed point captures expansion forces and prevents the pipe from shifting downward.
Between fixed points are sliding clamps, which allow vertical movement during expansion.
The penetration through the ceiling must be equipped with a sleeve or a flanged bushing, which allows pipe movement without transferring forces to the building structure.
Ventilation of the riser above the roof (minimum 500 mm above the roof level, at least 1 m away from windows) is essential – without it, a vacuum forms during flushing, which sucks water out of the trap seals of the fixtures.

Connecting fixtures to the riser

Fixtures (toilet, sink, bathtub...) are connected to the riser via branch fittings – either direct branch fittings (45° or 88.5°) or angled double-socket branch fittings. A toilet is connected directly via a DN110 elbow or an angled branch DN110/110. A sink, shower, and kitchen sink are connected via shorter horizontal pipes (DN50 or DN75) with the appropriate slope.

For more information on the correct slope of horizontal drainage pipes, read the topic Slope of HT drainage pipes: what angle is correct and why it matters.

Step 4: Installation of horizontal collection pipes

Horizontal pipes – that is, horizontal sections that collect waste from multiple fixtures to the riser or directly to the connection – are installed from top to bottom following the direction of flow, but you can physically install them from the connection point (from the riser or connection) towards the fixtures. Reason: the socket openings of the fittings must face against the direction of water flow (i.e., the socket is always "down" in the direction of flow). This ensures that the edge of the socket is not exposed to the impact of flowing water and dirt does not tend to penetrate the connection.

Slope of the horizontal pipe: the standard STN EN 12056 recommends a minimum slope of 1 % (1 cm per 1 m) for DN 50–110. In practice, an ideal slope of 1.5–2 % provides sufficient flow speed (min. 0.7 m/s for self-cleaning effect) without the risk that water drains faster than solid matter and leaves behind sediment. An excessively steep slope (over 4–5 %) conversely causes water to run off while solid matter remains, which is paradoxically worse.

A detailed calculation of the slope and practical examples can be found in the topic Slope of the drainage pipe HT: what angle is correct and why it matters.

Installation of cleaning fittings

We recommend installing an HT cleaning fitting on each longer horizontal section (over 4–5 m) and on each vertical riser. This is a fitting with a side opening equipped with a screw-on cap, which allows inserting a cleaning hose or a spiral cable in case of a blockage without the need to disassemble the pipe.

Install the cleaning fitting so that its inspection opening is accessible – not embedded in concrete, not hidden behind a fixed drywall partition. Access to cleaning fittings must be solved by inspection covers or sliding panels. On a vertical riser, the cleaning fitting is usually installed at the lowest point before the horizontal elbow in the floor level.

More on the use of cleaning fittings can be found in the topic How to use an HT cleaning fitting and a blockage fitting during pipe inspection.

Step 5: Changes in direction – correct use of elbows

Changes in direction are inevitable in drainage pipes, but they must be designed to minimize hydraulic resistance and not retain debris. For gravity drainage, the following principles apply:

On horizontal pipe never use a 90° (88.5°) elbow in the horizontal plane. Such an elbow stops the flow and creates a catch point for debris. Use two 45° elbows with an intermediate section, or special directional fittings with a longer arc radius.
On the transition from horizontal to vertical (i.e., down to the riser) an 87° (88.5°) elbow is acceptable, as it utilizes gravity.
For WC the standard is HT elbow DN110 87° with a neck for connecting the WC bowl. These elbows are designed to directly accept the waste neck of the WC bowl with a seal.
Chaining of elbows: never chain two 87° elbows directly after each other in the horizontal plane (S-bend) – this creates a hydraulic barrier. If an S-shape is needed, use a flexible coupling or a long arc.

Step 6: Reducers and transitions between diameters

When the pipe diameter changes – for example from DN50 (basin) to DN110 (riser) – you use an HT reducer. The reducer must be oriented correctly: the larger diameter is always on the side of the riser (in the direction of flow), the smaller on the side of the appliance. Never reduce the flow direction – i.e., from a larger to a smaller diameter in the direction of flow – this would create a pressure point and cause problems during intensive flow.

When connecting multiple devices of different diameters to a common horizontal pipe, proceed by first connecting the device with the smallest diameter and gradually increasing to the diameter of the main pipe. For example: basin DN50 → connection to DN75 pipe via a reducer → sink DN50 → pipe DN75 → riser DN110 via a diagonal branch.

In places where confusion or incorrect installation could occur, you can use an HT plug to temporarily close an unused fitting neck. Plugs are usually rubber or screw-on PP and are part of the finishing work also during pressure tests.

Step 7: Anchoring and support of the pipe

Anchoring is critically important for two reasons: it prevents sagging of the horizontal pipe (which would disrupt the slope) and dampens vibrations and noise from flowing water. Clamps and hangers should be made of a material compatible with PP – ideally plastic or with a rubber insert, not bare metal (contact between metal and PP during expansion damages the pipe surface and causes vibration noise).

Anchoring intervals for horizontal pipe:

DN 32 – max. 0.5 m
DN 40 – max. 0.6 m
DN 50 – max. 0.8 m
DN 75 – max. 1.0 m
DN 110 – max. 1.1–1.2 m

For long horizontal sections in the ceiling or in wall grooves, you must address expansion: every 6–8 m install an expansion gasket or ensure that one of the joints has a larger insertion gap (maximum insertion minus 15 mm instead of minus 10 mm). On both sides of this "expansion point" there are fixed anchors, with sliding anchors in between.

Step 8: Pressure test and inspection before covering

Before covering the pipe with drywall, adhesive compound, screed layer, or otherwise making the route inaccessible, always perform a pressure (or load) test. For gravity drainage, it is a water test: close all openings with plugs (HT plugs are ideal for this), fill the pipe with water and let it stand for 30 minutes. Inspect all connections visually – a drop in water level or wet spots indicate a leak.

There is also a smoke test (you inject pressurized smoke into the system and look for places where the smoke escapes) and a vacuum test (using special equipment). For standard apartment or residential construction, a water load test is sufficient.

Important places to inspect separately:

Every connection between the neck and the pipe – visually and by tapping (a hollow sound indicates an improperly seated gasket)
Reducers and transitions between diameters
Places passing through walls and ceilings
WC elbow connection – leaks occur most frequently here if the WC is not properly screwed in
Closure of cleaning fittings

Step 9: Connection of appliances – WC, basin, shower, bathtub

A WC bowl is connected to an HT elbow DN110 via a rubber gasket or directly with a waste neck hose from the WC to the elbow neck (depends on the model of the WC). The elbow must be installed in the floor or on the wall in the correct position even before tile laying – subsequent correction is very laborious. The correct height and position of the elbow relative to the final floor is crucial: most WC bowls have a waste neck at a height of 180 mm from the bottom edge of the bowl for a wall-hung WC, and varies for a pedestal model.

The sink, bidet, and shower are connected via a trap (seal, so-called geruchverschluss) – this retains the smell from the sewer. The trap has an outlet DN40 or DN50, which is connected to the HT pipe with the corresponding diameter. Make sure that the trap has a water seal height of at least 50 mm (standard STN EN 1253) – shallow traps evaporate during long periods of non-use and allow odors to penetrate.

The washing machine and dishwasher are connected via a direct discharge trap (height 40–50 mm) to a DN50 pipe. Never connect them directly without a trap – the pump discharges water under pressure and can cause back-siphonage and contamination.

Step 10: Finishing work, ventilation and inspection

After testing all the devices, check the functional ventilation of the stack. The simplest test: flush the toilet and observe whether you can see bubbles or smell odors in the adjacent sink. Bubbles in the sink trap during a toilet flush indicate a vacuum – the system is not sufficiently ventilated and is drawing air from the traps. The solution is either to extend the vent pipe above the roof or to install an air admittance valve (AAV) on the stack at the top floor.

Document the entire installation: photographs of the route before covering, a layout plan of inspection and cleaning points, the used diameters and materials. This documentation is invaluable in the case of any future fault or renovation. For more on common faults and their solutions, see the topic Common faults in HT waste systems and how to fix them.

Typical errors from practice and how to avoid them

Over the years of working with customers and plumbers, we have identified several recurring errors that cost homeowners nerves and money:

Forgotten expansion gap – the pipe "waves" between clamps, joints expand and contract during the winter until permanent deformation occurs.
Too many elbows in a row without ventilation – each 88.5° elbow is approximately equivalent in hydraulic resistance to 2 meters of straight pipe. Chaining three such elbows is equivalent to 6 meters of extra length.
Insufficient slope

– most commonly occurs during installation under the ceiling, where space is limited. The plumber sacrifices slope for height above the floor, resulting in almost horizontal pipe with a slope of 0.2 %.
Wrong orientation of the socket – the socket must face AGAINST the flow of water. If it is turned in the direction of the flow, the edge of the socket catches debris and the pipe clogs more quickly.

Using fat instead of vaseline – animal fats, margarine and similar improvisations cause degradation of rubber seals over months.

Missing cleaning piece – during the first clog, the plumber will charge for dismantling the wall instead of a simple cleaning access.

Wrong socket for the toilet – using a straight elbow instead of an angled one, or confusing 87° and 45° elbows, leads to the toilet bowl not fitting properly or the waste not flowing.

Correct joining techniques – recap

The topic of correct joining techniques is so extensive that we dedicate a separate article to it: How to correctly connect HT pipes, elbows and tees without leaks. Here we summarize the most important points:

Always check the gasket before installation – cracked, deformed or protruding gaskets must be replaced immediately

The smooth end of the pipe must be free of burrs, straight cut, and without cracks

Vaseline is applied only to the smooth end, not into the gasket groove

Insertion must always be perpendicular to the axis, not at an angle

Expansion gap of 10 mm must always be preserved after insertion

Never fill the joints with silicone or sealant – the gasket is designed without additional modification and any additional sealing interferes with expansion

Most frequently asked questions (FAQ)

Can I glue the HT pipe instead of inserting it into the socket?

No. The HT system is exclusively a push-fit system with rubber gaskets. There is a PVC waste system (older type, less common today) that uses glue, but the HT PP material does not bond properly with standard PVC glue and the joint would be leaky. Even if you used special PP glue, the pipe would lose its expansion flexibility and cracking would occur.

How deep should I insert the pipe into the socket?

Before installation, draw a pencil line on the smooth end of the pipe at a distance equal to the insertion depth (according to the table for the given diameter). Insert the pipe until the line aligns with the edge of the socket – then pull it back by 10 mm. This 10 mm gap is the expansion space. Some fittings have an internal stop (limit) inside the socket, which helps with correct positioning.

How long can a horizontal pipe be between the device and the stack?

The standard STN EN 12056-2 limits the length of the connecting branch (without a vent pipe) for various devices. For a sink and bidet, it is max. 1.7 m for DN 40, max. 3.0 m for DN 50. For a shower and bathtub, max. 3.0 m for DN 50. For a toilet, the connecting pipe is DN 110 and the maximum length without a vent loop is 2.0 m – longer runs require a vent pipe or an air admittance valve. If you exceed these values, siphoning of the trap during flushing may occur.

What to do if the HT pipe runs through a load-bearing wall?

The passage through a load-bearing wall must be solved with a steel sleeve (penetration) with a larger diameter than the pipe, to ensure space for expansion and to prevent forces from the pipe from being transferred to the wall. The gap between the pipe and the sleeve is filled with soft mineral wool or a special fire-rated gasket (if it is a fire-separating construction). The pipe must never be directly embedded in the wall structure without a sleeve.

Is it necessary to insulate the HT pipe?

For standard internal waste pipes in heated rooms, thermal insulation is not necessary from a functional point of view. However, acoustic insulation is recommended – wrapping the pipes with acoustic insulation foam or installing them in a cavity wall with sound insulation – especially for stacks running through living rooms or bedrooms. In unheated areas (attic, cold corridor), thermal insulation is necessary for routes where freezing of the pipe content could occur.

Can I connect the washing machine directly to the HT pipe without a trap?

No. The washing machine must be connected via a trap, as the machine’s pump creates pressure during drainage. Without a trap (or without backflow protection), a siphon effect can occur – water from the toilet flush can flow back into the washing machine or vice versa, the drained water from the washing machine can enter the waste system with excessive pressure, which can push out the rubber seals. The standard solution is a floor or wall-mounted washing machine trap DN 50.

Conclusion: HT pipe installed once and correctly

The installation of the HT waste pipe is not technically demanding, but it requires a systematic approach. Each step – from planning the route and selecting the correct diameters, through precise cutting and greasing of the gaskets, to the correct slope and placement of inspection points – affects how the entire system will function for decades. An experienced plumber performs these steps automatically and quickly, but that does not mean they do them any differently than we have described in this article.

If you plan to install it yourself, we recommend studying the topics How to correctly connect HT pipes, elbows and tees without leaks, Cleaning and maintenance of HT pipes: how to avoid clogging and Common questions about the HT waste system – these articles will provide further context for making the right decisions in various situations. And if you are unsure about a specific detail when choosing materials, always look at the relevant products in the category Waste system HT – product parameters are listed there including dimensional data you need for planning.

Do you have a question about this topic?

Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.

Name and surname Do not fill in this field:

Email

Message