A siphon may seem like a simple and insignificant detail, but its selection directly impacts whether your kitchen or bathroom will suffer from blockages, leaks, and unpleasant odours. Apartments, compared to private houses, present several unique considerations: narrow cabinet spaces, a shared sewage riser, and the influence of neighbouring apartments on the drainage system's pressure.
In this guide, we'll explore all major siphon and trap types found in apartments — from sinks and baths to shower enclosures and floor drains — and explain the criteria for making your choice. This guide focuses on selection and installation prerequisites, not daily maintenance — for cleaning and maintenance tips, please read our separate article on siphon maintenance.
If you're planning a bathroom or kitchen renovation in an apartment in Tallinn or Harjumaa, it's wise to consider siphon and trap choices before ordering furniture, as cabinet dimensions often dictate which siphon type is suitable.
This article provides practical criteria to help you make an informed decision or at least communicate knowledgeably with your installer.
Why is Siphon Choice so Important in an Apartment?
The primary role of a siphon, or water trap, is to prevent sewage gases from entering the living space while allowing wastewater to drain freely. The wrong type, size, or installation height can lead to three common problems: slow drainage, blockages, and unpleasant odours.
In an apartment, an additional factor comes into play — the shared riser. When many apartments drain water into a single pipe simultaneously, a momentary negative pressure can occur, drawing the water trap dry. Consequently, when selecting a siphon for an apartment, it's advisable to favour solutions with a deeper water trap and, if necessary, consider a variant with a vacuum valve.
What are the Main Siphon Types and When Should They Be Used?
Several main types of siphons are available on the market, differing in shape, space requirements, and intended use.
Bottle Siphon (Classic Siphon)
The bottle siphon is the most common solution for sinks and washbasins. Its advantage lies in easy dismantling and cleaning – simply unscrewing the bottle-shaped part. The water trap depth is usually sufficient even for apartment building conditions.
- Suitable for cabinets with deeper space (typically at least 15–18 cm free height)
- Easy to clean without disassembling pipes
- Available in chromed brass or white plastic (PP)
Shallow Siphon (Low-Profile Siphon)
The shallow siphon is designed for low cabinets where a bottle siphon won't fit. Its height can be as little as 6–8 cm, but this also means a smaller water trap volume, requiring more frequent checks to ensure water doesn't evaporate (e.g., in a rarely used bathroom).
- The only viable solution for very shallow cabinets or wall-mounted basins
- Smaller water trap dries out faster during longer periods of disuse
- Cleaning is slightly more complex than with a bottle siphon
Dry Siphon and Vacuum Valve (Mechanical Water Trap)
A dry siphon uses a membrane or valve instead of water, which only opens when water flows through and otherwise closes completely. This resolves the evaporation problem and is well-suited for infrequently used drains, such as guest WCs, summer cottage sinks, or floor drains that are rarely used.
In an apartment building, a dry siphon or a solution augmented with a vacuum valve is a sensible choice where you want to ensure protection against sewer odours, even if the water trap should empty due to vacuum.
- Does not dry out or empty due to vacuum
- Suitable for seasonal use (summer house, guest room)
- Membrane requires periodic inspection as it can wear over time
Shower Trap vs. Floor Trap — What's the Difference?
For bathroom floor drains, you must choose between installing a linear (channel-type) shower trap, a round floor trap, or a shallow trap hidden under the shower enclosure.
- Always check that the depth of the trap's water seal meets manufacturer and standard requirements (generally at least 50 mm)
- Prefer traps whose water seal component can be removed for cleaning without tools
- If the bathroom is used infrequently, consider a trap with a dry water seal
Classic Floor Trap
Round or square floor traps are suitable for most bathrooms and are the most common choice in apartments. Their water trap is typically removable and cleanable from above, without damaging the floor.
Linear Shower Trap
A linear trap is usually positioned along the edge of the shower enclosure and allows for floor gradient in only one direction, simplifying tiling. In an apartment, before selecting, you must check if the existing intermediate floor and drain pipe location allow for sufficient slope — otherwise, water will collect near the trap.
How to Account for Siphon Height in Low Cabinets?
Before ordering cabinet furniture, you should always measure the available space between the basin's drain opening and the bottom of the cabinet. This is the most common mistake that necessitates replacing a siphon retrospectively.
If the furniture is already in place and space is limited, a shallow siphon is often the only workable solution. However, if you're still planning your renovation, it's wise to allow sufficient clearance when choosing cabinets – this gives you the freedom to opt for a higher-quality and easier-to-maintain bottle siphon.
- Measure the free height from the drain opening to the cabinet base before ordering furniture
- For a bottle siphon, ideally allow at least 15–18 cm of free space
- A shallow siphon typically needs 6–10 cm, but exact measurements vary by manufacturer
- Corner basins and wall-mounted basins often require a special corner siphon
Which Drain Opening Diameter is Suitable for Which Appliance?
The diameter of the siphon and drain pipe must match the volume and speed of water draining from the appliance. An incorrectly sized siphon is a frequent cause of blockages and slow drainage in apartments.
- 32 mm — washbasin, smaller sink
- 40 mm — kitchen sink, baths, shower enclosures, washing machine, and dishwasher
- 50 mm — floor traps and larger basins
- 50–110 mm — WC connection according to the sewage riser diameter
Chromed Brass or White Plastic (PP) — Which Material to Choose?
Siphons are mainly produced from two materials: impact-resistant polypropylene (PP) and chromed brass. Both have their advantages, and in an apartment context, the choice depends primarily on visibility and budget.
PP Plastic
Plastic siphons are lighter, cheaper, and sufficiently durable for general use. They are well-suited for concealed solutions inside cabinets where aesthetics are not paramount.
Chromed Brass
Brass siphons are more aesthetic and typically used where the siphon is visible, such as under a designer basin without a cabinet. They are more resistant to mechanical stress but are more expensive.
How to Connect an Overflow, Washing Machine, and Dishwasher to a Siphon?
Most baths and some basins have an overflow opening that must be correctly connected to the siphon to prevent water overflow onto the floor in case of appliance malfunction. This is done using a special siphon with an overflow pipe, which has a separate fitting for the overflow hose.
Washing machine and dishwasher drains must not go directly into the sewer but must be connected to the siphon via a special fitting (a 'machine fitting') which has its own non-return valve. This prevents sewage water from flowing back into the machine and eliminates odour formation.
- Check that the siphon has a dedicated fitting for the washing machine or dishwasher hose
- For baths with an overflow, use only a siphon with an overflow fitting
- Do not connect two high-volume appliances (e.g., washing machine and dishwasher) to the same fitting simultaneously
Why Do Noise or Odour Occur from a Siphon with an Insufficient Water Trap?
If the water trap depth of a siphon is too shallow, or if the water evaporates from it, a direct connection forms between the room's air and the sewer pipe. The result is a characteristic sewer odour, which is usually stronger in the mornings when the water has partially evaporated over 24 hours.
Noise, such as a gurgling or bubbling sound in the drainpipe, may indicate that the siphon or riser ventilation is not functioning correctly, and the water flow creates negative pressure that causes the water trap to vibrate. In such cases, a siphon augmented with a dry water seal or inspection of the existing ventilation system typically helps in apartments.
- For infrequently used basins, choose a siphon with a dry water seal
- If odour occurs regularly in a specific spot, check the water trap depth and water level
- Repeated gurgling likely indicates a riser ventilation problem, not the siphon itself
What Else Should Be Considered in an Apartment Building?
An apartment building's sewage system differs from a private house primarily because many apartments share a common riser. This means that your siphon's behaviour is also affected by your neighbours' water usage.
If you live in an older apartment building in Tallinn or elsewhere in Harjumaa, where risers are decades old, there may be deposits that reduce flow capacity and create greater pressure fluctuations than usual. In such a case, it makes sense to choose a siphon with a slightly deeper water trap and, if necessary, discuss the riser's condition with the apartment association.
- In a renovated apartment building, the ventilation riser might be missing or blocked, increasing the risk of vacuum.
- When renovating, it's worth simultaneously reviewing the condition of old pipes — read more about old cast iron pipes.
- If drainage is slow or repeated blockages occur, the siphon may not be to blame, but rather the riser itself.
What to Consider When Choosing a WC Pan Drainage Connection in an Apartment?
The connection of a WC pan to the sewage riser differs from a standard siphon in that most WC pans have a water trap built into the pan's design, so a separate siphon is usually not used. However, the correct selection of a connecting collar or sealing gasket is crucial, as it connects the pan's outlet to the sewer pipe.
In an apartment building, where pipe diameters and locations may differ from manufacturer standards, a collar of appropriate length and angle must be chosen – a collar that is too short or installed at the wrong angle can cause leaks at the base of the pan or insufficient drainage, which in turn increases the risk of blockages.
If you are replacing an old WC pan with a new one, it's also worth checking the location of the floor or wall outlet and ensuring that the new pan's dimensions are compatible with the existing connection point; otherwise, adapter pieces or repositioning the connection point may need to be considered.
- Before purchasing a new WC pan, check the location and type of the existing drain connection (to the floor or wall)
- Use a high-quality, flexible collar that can withstand minor shifts without leaking
- Avoid over-tightening when securing the pan, as this can compress the collar and restrict drainage
How to Choose Siphons When Renovating a Bathroom and Kitchen Simultaneously?
During a major renovation where a bath, basin, and kitchen cabinets are all being replaced at once, it's advisable to approach siphon selection holistically, rather than for each appliance separately. Since all these drains may eventually lead to the same riser, the choice in one area indirectly affects the performance of others — for example, if one connection point has too narrow a diameter, it can slow down the drainage of the entire branch under higher load.
With a holistic approach, it makes sense to compile a list of all drain points, including their diameter, cabinet height, and frequency of use, and select the appropriate siphon type for each based on this, rather than randomly from what's available in stores. This approach prevents a situation where one wrong choice leads to additional repair needs within a few months. If you plan to replace the siphon yourself, ensure before purchase that the new product's connection details precisely match the existing plumbing, as manufacturers' measurements can vary slightly even for products with the same name.
If the renovation also involves updating the plumbing itself, it's worth considering the riser's ventilation and diameter suitability for the load of new appliances, especially if an additional bathroom or utility room, which was not previously present in the house, is being added.
What Are the Signs That an Existing Siphon in an Apartment Should Be Replaced?
Even if a siphon isn't visibly leaking, several signs may indicate that it should be replaced soon rather than waiting for a failure to occur.
- The siphon was manufactured more than 10–15 years ago, and the material has become brittle or discoloured.
- Nuts have repeatedly required tightening, indicating thread wear.
- Drainage has become slower, although cleaning has not resolved the problem.
- A regular gurgling or squelching sound is heard from the siphon.
- A faint but persistent damp smell is present in the cabinet, even if no visible water is found.
What Practical Tips Should Be Followed During Siphon Installation?
Even the correct siphon choice doesn't guarantee a good result if installation is done carelessly. A few simple rules help avoid later leaks and blockages.
- Always use the provided gaskets, not silicone, as a sealant — silicone makes later disassembly difficult.
- Do not overtighten plastic fittings; this can strip the threads.
- After installation, check for leaks by running water for at least 15–20 minutes.
- Leave access below the siphon so that subsequent cleaning or replacement is possible without damaging furniture.
Does the Siphon Type Affect Drain Environmental Friendliness and Maintenance Needs?
The choice of siphon affects not only the risk of leaks and odours but also how often the drainage system needs maintenance and what cleaning products are used. An easily accessible bottle siphon with a removable base allows for regular mechanical removal of accumulated hair, food residue, and grease without chemical cleaners, which is a more environmentally friendly solution and kinder to plumbing seals.
Shallow siphons and narrower diameter solutions often have less internal volume, meaning debris accumulates to a critical amount more quickly, and they need more frequent cleaning to prevent blockages. If the goal is to minimise the use of chemical cleaning agents, it's worth choosing a siphon that can be easily opened and cleaned by hand.
In the long run, a higher-quality and slightly more expensive siphon is often a more economical choice, as it lasts longer, requires less frequent parts replacement, and doesn't repeatedly create waste from old broken components. If you're unsure whether your existing siphon still meets your apartment's needs, the surest way is to have a specialist inspect it along with the rest of the drainage system, rather than just checking the visible part.
Summary: How to Make the Final Choice?
Choosing a siphon for an apartment comes down to three questions: how much space is under the cabinet, what is the water volume of the draining appliance, and how often is the drain used. A shallow siphon suits a narrow cabinet, a dry siphon for an infrequently used basin, and a standard bottle siphon for a regular kitchen or bathroom basin.
If the choice seems complex, or if recurring problems with odours, noise, or slow drainage occur in the apartment building, it's wise to involve a professional who can assess the condition of both the siphon and the broader drainage system.