How to Use HT Cleaning Piece and Plunger Fitting During Pipe Inspection
Cleaning piece and plug fitting in the HT system: everything you need to know before pipe inspection
Every drain pipe gets clogged, silted up or simply needs to be checked at some point. And that's exactly when you find out whether the system was designed and built correctly – that is, whether there are inspection openings where they are needed and whether the fittings installed are ones that allow for convenient work. Two key elements that make every inspection possible without demolition and cutting are the HT cleaning piece and the plug fitting (also called a blind plug or inspection plug). In this article, we will go through in detail what these fittings are, where to install them, how to work with them during an inspection and what to pay attention to in order to complete the work without unnecessary complications.
What is an HT cleaning piece and why it is indispensable in the plumbing system
An HT cleaning piece is a fitting installed directly into the drain pipe route, which allows access to the inside of the pipe without the need for its disassembly. It consists of a body with a side or front neck, into which a plug insert is inserted – most often a rubber or shortened plastic plug. After opening this plug, an access opening is created through which a cleaning spiral, a hose cleaner or an endoscopic camera can be inserted.
In practice, we distinguish several basic types of cleaning pieces according to the direction of access:
- Inline cleaning piece – a fitting in a straight axis, the access opening is in the extension of the pipe. Suitable for vertical stacks and for horizontal sections where we want to clean in one direction along the flow of waste.
- Side cleaning piece – access is perpendicular or at an angle of 45° to the axis of the pipe. Used where direct access is not possible due to the space layout.
- Corner cleaning piece (90°) – combines the function of an elbow and a cleaning piece. The access plug is located on the outer arc of the fitting. Saves space and replaces the combination of an elbow + inline cleaning piece.
Standard cleaning pieces are manufactured in sizes DN 50, DN 75 and DN 110 – which corresponds to the standard diameters of drain pipes for sinks, showers, baths and toilets. On the main stack pipe (DN 125 or DN 160), they are used less frequently, but are essential on long routes without natural access.
Plug fitting: the difference between temporary blinding and permanent closure
The term "plug fitting" is used in practice for several different products, so it is important to distinguish what we are talking about:
- Inspection plug (insert into the cleaning piece) – a rubber or plastic plug inserted into the opening of the cleaning piece. It can be opened and closed repeatedly. It is not primarily designed for permanent blinding, but for access during inspections.
- HT plug (permanent blinding fitting) – a solid HT plug slipped onto the neck of the HT pipe using a rubber gasket. Used for temporary blinding of the neck during phased installation or for permanent blinding of unused branches.
- Balloon plug (temporary) – an inflatable rubber balloon that is inserted into the pipe and inflated, thus temporarily closing the flow during a pressure test or cleaning. This is not a standard HT fitting, but a service tool.
In the context of pipe inspection, we are primarily interested in the inspection plug as part of the cleaning piece and the HT plug as a means of temporary blinding of the pipe during work. Both complement each other and each performs a different function at a different moment of the inspection.
Where exactly to install the cleaning piece: rules for design and installation
This is a topic that is most often neglected during custom installation. The cleaning piece is seen as "something extra", which costs a few euros and takes up space. When you come to clean a clogged pipe in five years and there is no cleaning piece, the situation suddenly becomes complicated and expensive.
Basic rules for placing the cleaning piece:
- At the beginning of each long horizontal section – for routes longer than 6–8 meters, there should be a cleaning piece at the entrance to the horizontal section, so that the entire route is accessible without disassembly.
- Before each change of direction (90°) – deposits form fastest behind elbows, so access before the elbow (HT elbow) is logical and practical.
- On the return piece of the vertical stack – the place where the vertical stack transitions into the horizontal collection pipe is extremely stressed and prone to settling of solid waste.
- In the basement before the entry into the sewer connection pipe – if the entry into the public sewer is deep or difficult to access, a cleaning piece before this location will save digging.
- On each floor in multi-storey buildings – the vertical stack should have a cleaning piece on each floor, ideally at a height of 0.5–1.0 m above the floor (comfortable working height).
- Behind each inlet junction of multiple devices – behind branches where WC, sinks and baths are fed at the same time, there is increased load and risk of clogging.
The standard STN EN 12056-2 (gravity drainage systems in buildings) does not strictly define the exact distances between cleaning fittings, but the recommended maximum distance is 15 m for horizontal sections and 10 m for vertical drops. In practice, experienced plumbers install a cleaning fitting every 10 m or at each major change in direction – and this is the correct approach.
Step-by-step procedure for pipe inspection with a cleaning fitting
We will describe a realistic scenario: you have a residential house with two bathrooms on the ground floor and a laundry room in the basement. The main DN 110 drop pipe runs from the basement ceiling into a manhole. The laundry room has stopped draining and an unpleasant smell has appeared under the kitchen sink. A cleaning fitting is installed on a bend in the basement drop and another one is located before the manhole entrance.
Step 1: Locating the problem before opening the cleaning fitting
Before you reach for the cleaning fitting, determine where the problem is. The symptoms indicate a blockage somewhere in the horizontal drop pipe between the laundry room and the manhole entrance – since the laundry room is not draining, but the toilet upstairs is working normally. If the upper floor drainage was not working, the problem would be higher up. This logic will save you time and unnecessary work.
Step 2: Preparing the work area and tools
Before opening the cleaning fitting, prepare the following:
- A bucket and rags – residual water will always flow out when you open the plug.
- Drain cleaning augers (manual or electric DN 100 for DN 110 pipe).
- A flashlight or headlamp.
- Rubber gloves and safety goggles.
- A replacement rubber gasket for the cleaning fitting – in case the original one is worn out.
Step 3: Opening the cleaning fitting
The shortened plastic plug is unscrewed counterclockwise. The rubber gasket is pulled out directly. Note: in the case of a horizontal pipe, there will be water under pressure behind the plug – hold a bucket underneath before fully unscrewing. In a clogged pipe, there may also be a fat plug that comes out partly solid – unpleasant, but normal.
Step 4: Inserting the auger and cleaning
Insert the cleaning auger slowly, without forceful movements. With a manual auger, you turn the handle while pushing forward. With an electric auger, set low revolutions (first pass through resistance). When you feel resistance, alternate the direction of rotation – not always a hard deposit, sometimes it is a wad of paper or wet rags twisted into a ball. When the auger breaks through, there will be a sudden drop in resistance and the water will start to drain.
Step 5: Flushing and verifying the flow
After removing the auger, fill the nearest appliance (laundry room drain or a shower) and let it drain. Watch the flow through the open cleaning fitting to see if the water passes freely. If yes, the pipe is clear. If it still does not drain well, the problem may be behind another cleaning fitting or in the manhole – proceed to the next access point.
Step 6: Closing and checking the seal
Before screwing the plug back in, check the condition of the rubber gasket. An old gasket is dry, cracked or stiff – in such a case, replace it. Lightly moisten the new gasket with soapy water (not oil – oil damages EPDM rubber). Screw the plug in by hand and then gently tighten with a wrench, do not over-tighten – the plastic can crack. After closing, run a test flow and check the seal at the plug.
HT plug for pressure testing and phased installation
Besides the inspection itself, the HT plug is also indispensable during construction and phased installation. Let us describe two real-life examples from practice:
Example 1: Rough construction, completing bathrooms in phases
Imagine a new residential house where the rough installation of the waste pipe is complete, but the bathroom will be finished in three months. All unfinished flanges of HT pipes and branches must be temporarily sealed. The reasons are practical: to prevent the entry of mortar, dry mixes, concrete chips and other construction materials into the pipe; to prevent the escape of odors from connected pipes; to prevent the entry of rodents through open flanges (not a joke – it happens).
The HT plug is simply slipped over the pipe neck in the same way as any other HT fitting – the rubber gasket ensures air and watertightness. When it is time to complete the installation, you simply remove the plug and replace it with the correct elbow, trap or connecting pipe.
Example 2: Pressure tightness test before embedding
Before covering the drain pipe in the floor or wall, it is reasonable (and mandatory for larger buildings) to perform a water tightness test. The procedure is simple: all pipe outlets are sealed with HT plugs, water is poured into the system through the highest unsealed neck, and it is left to stand for at least 30 minutes. A drop in the water level indicates a leak.
During this test, you must ensure that the plugs can withstand the hydrostatic pressure of the water column. A standard HT plug in standard configuration can withstand a pressure corresponding to a water column height of about 3–5 meters (0.03–0.05 MPa), which is sufficient for a standard apartment installation. For taller buildings or special tests, tighter mechanical plugs with a wedge closure are used.
Most common mistakes when working with the cleaning piece and the clog trap fitting
After years of practical experience, the same mistakes keep repeating. Here are those that lead to the highest repair costs:
- Placing the cleaning piece in an inaccessible location – a cleaning piece embedded in the wall without a maintenance opening is practically useless. Always ensure access of at least 25 × 25 cm (ideally 30 × 40 cm) for comfortable work.
- Over-tightening the screw plug – plastic cracks when over-tightened, the gasket deforms and the plug stops sealing. Tightening "firmly by hand + a quarter turn with a wrench" is the maximum.
- Using an unsuitable lubricant – vaseline, motor oil and oil-based silicone sprays damage EPDM rubber gaskets. Only soapy water or special silicone lubricant based on rubber is suitable.
- Forgetting the plug during staged installation – an open pipe neck clogged with mortar is one of the worst problems when starting the system. It costs several times more to fix than to prevent.
- Placing the cleaning piece directly after the WC – when cleaning the pipe after the WC, you must have free access of at least 40–50 cm from the toilet bowl. A cleaning piece directly after the WC elbow does not allow the spiral to be inserted into the correct position.
- Neglecting regular gasket inspection – rubber gaskets in cleaning pieces should be visually inspected every 5–7 years and replaced at the first suspicion of an odor leak. Replacing the gasket costs a few cents, repairing mold in the wall costs thousands.
Dimensioning the cleaning piece: which diameter for which device
The basic rule is simple: the diameter of the cleaning piece must match the diameter of the pipe it is installed on. There must be no reduction in the flow diameter. Specific values:
| Device | Minimum pipe diameter | Cleaning piece DN | Access opening (min.) |
|---|---|---|---|
| Basin, bidet | DN 50 | DN 50 | Ø 44 mm |
| Shower, bathtub | DN 50 – DN 75 | DN 50 / DN 75 | Ø 44 – 67 mm |
| WC, washing machine | DN 110 | DN 110 | Ø 100 mm |
| Collection (drain, floor) | DN 110 – DN 125 | DN 110 / DN 125 | Ø 100 – 113 mm |
| Main building drain | DN 160 | DN 160 | Ø 148 mm |
If the cleaning piece is installed on a reducer (e.g. transition from DN 110 to DN 75), always install the cleaning piece on the side of the larger diameter. Why? Because the cleaning spiral is inserted in the direction of flow (from larger to smaller) and this way you always have access to the critical point – the reducer and the section behind it. More about system reductions can be found in the section devoted to HT reduction.
Cleaning piece and clog trap fitting in combination with other HT fittings
In a real installation, the cleaning piece does not work in isolation – it is part of the system. Let's look at a few typical configurations from practice:
Configuration 1: Vertical drain with cleaning piece on the return elbow
A classic situation in an apartment building: a vertical waste drain DN 110 runs from the basement ceiling into a horizontal pipe. At the bend (return elbow), an HT 87° elbow is installed and immediately after it a cleaning piece DN 110. This configuration allows cleaning of the vertical drain from above (through the roof vent) and from below (through the cleaning piece in the basement). A spiral can be inserted in both directions and the entire drain route is covered.
Configuration 2: Horizontal pipe with two cleaning pieces
A long horizontal pipe DN 110 (e.g. 12 meters) has a cleaning piece at the beginning and at the end. In between is one HT 30° elbow for route correction. If a problem occurs anywhere on this route, the first 6–7 meters are covered from the starting cleaning piece, the rest from the end one. No section remains inaccessible.
Configuration 3: WC with cleaning piece after the elbow
After the WC elbow (HT 87° elbow), a short section of HT pipe (min. 30 cm) follows and then a cleaning piece DN 110. The pipe continues further to the drain behind the cleaning piece. This configuration allows to remove clogs directly after the WC without having to manipulate the toilet itself.
Material, temperature and chemical resistance of HT fittings
The HT system is made of polypropylene plastic PP-HM (homopolymer propylene with high molecular weight). This material has a long-term operating temperature of up to 95 °C and can withstand up to 100 °C in the short term. For household waste pipes (dishwashers, washing machines, normal hot water) this is more than sufficient.
The rubber seals in the cleaning fittings and HT plugs are standardly made of EPDM rubber (ethylene-propylene-diene rubber), which is resistant to:
- Temperatures from -40 °C to +110 °C (short-term peaks).
- Common household cleaning agents, acids and bases in normal concentrations.
- Ozone and UV radiation (relevant for outdoor installation).
What EPDM does not tolerate: mineral oils, aliphatic hydrocarbons, benzene and concentrated organic solvents. If larger amounts of such substances regularly flow through the pipe (e.g. from an auto service), it is necessary to consider more durable seals or a different system. However, this is not a problem for normal residential and family housing.
Related topics can also be found in the article "Cleaning and maintenance of HT piping: how to avoid clogging" and "Common faults in the HT waste system and how to fix them" in this Knowledge Centre.
Access to the cleaning fitting: inspection hatch and protection in the wall
One of the most unpleasant situations is when the cleaning fitting exists, but is built in without an inspection opening. This mistake is made during renovations, when the plumber installs the cleaning fitting correctly, but the bricklayer or plasterer simply covers it up.
Rule for proper implementation: each cleaning fitting must have an inspection opening in front of it with minimum dimensions of 25 × 25 cm (for DN 110), ideally 30 × 40 cm. The inspection opening must be either a permanent inspection hatch (plastic, stainless steel or tiled hatch), or a removable panel. It must not be permanently built in or occupied by furniture.
For installation in drywall, the solution is simple – during installation, a recess is left and after completion, the inspection hatch is installed. For installation in masonry, it is more complicated – an access opening must be planned in advance and a flap left. Cutting an inspection opening retroactively in a tiled wall is much more expensive than proper preparation from the beginning.
The topic of HT system design is discussed in more detail in the article "Installation of HT waste pipe step by step" and "How to properly connect HT pipes, elbows and tees without leakage" in this Knowledge Centre.
Most frequently asked questions (FAQ)
Must I have a cleaning fitting necessarily, or is it just a recommendation?
In single-family homes and apartment units, the installation of a cleaning fitting is not strictly required by law in every case, but the standard STN EN 12056-2 and design regulations for multi-storey buildings require it for long sections. In practice, however, every responsible plumber installs cleaning fittings – not because of the standard, but because without them, the pipe cannot be serviced without breaking. In larger apartment buildings and multifunctional buildings, their installation is part of the design documentation and the final inspection.
Can I open the cleaning fitting myself, or do I need a professional?
Opening a cleaning fitting is a simple operation that any skilled DIYer can handle. You need to have a bucket under the opening, protect your eyes and skin, and know what you are doing. Cleaning the spiral itself is also manageable at home for simple blockages. For long horizontal sections, neglected piping or repeated blockages, it is better to call a professional with an electric spiral and possibly a camera.
What to do if the plug of the cleaning fitting leaks?
Leakage at the plug of the cleaning fitting is most often caused by a worn or deformed rubber seal. First step: unscrew the plug, check the seal – if it is dry, cracked or deformed, replace it. Wet the new seal with soapy water and screw it back in. If the problem persists, check the thread of the plug and the internal thread of the cleaning fitting – if the thread is damaged, the entire cleaning fitting must be replaced.
What is the difference between an HT plug and an inspection plug in the cleaning fitting?
An HT plug is a separate fitting that is slipped onto the open mouth of the HT pipe – it is used for temporary or permanent blinding of an unused mouth. An inspection plug (insert) is part of the cleaning fitting – it closes the access opening of the cleaning fitting and can be repeatedly opened during each inspection. These are two functionally different components, although in practice the two terms are sometimes mixed.
Can I use a DN 110 cleaning fitting as a branch for a smaller diameter?
No, a cleaning fitting is not a substitute for a branch. It is an inspection fitting, not a dividing one. If you need to connect a sink to a DN 110 drain, use the correct HT branch with a reduction to DN 50. The cleaning fitting only serves as an access opening – the flow part is straight and does not contain a branch for another device.
How long does the rubber seal in the cleaning fitting last?
EPDM seals in the HT system have a service life of 15–25 years under normal operating conditions. Factors that shorten their life: frequent mechanical opening (more than 2–3 times a year), aggressive chemicals, temperatures above 80 °C or long periods without moisture (in little-used piping, the rubber dries out). It is recommended to visually inspect them during each inspection and to replace them preventively after 10–15 years or at the first signs of degradation.
Conclusion: investment in the right inspection elements always pays off
The cleaning fitting and the blockage fitting are a small item in the budget of every installation – in the order of a few euros per piece. But their absence will cost you much more: cutting into walls, removing tiles, dismantling cabinets and furniture. A properly designed HT waste system has inspection openings at every critical point, access to them is free and the seals are regularly checked.
If you are unsure whether your existing system is properly designed, the article "Frequently asked questions about the HT waste system" in this Knowledge Centre will help you identify potential weak points. And if you are installing a new system, don't forget to plan the placement of cleaning fittings already in the design phase – changing it later is expensive and unpleasant.
Do you have a question about this topic?
Not sure or dealing with a specific situation in your home? Write to us – we are happy to help.