At first glance, a siphon seems like a simple and insignificant detail, yet its choice directly influences whether your kitchen or bathroom suffers from blockages, leaks, and bad odours. Apartments, compared to detached houses, have several unique characteristics: narrow furniture cabinets, shared sewage risers, and the impact of neighbouring flats on drain system pressure.
In this guide, we will review all the main types of siphons and traps found in apartments – from kitchen sinks and baths to shower enclosures and floor drains – and explain the criteria for making the right selection. This guide focuses on selection and installation prerequisites, not daily maintenance. For cleaning and maintenance, please refer to our separate article on siphon care.
If you're planning a bathroom or kitchen renovation in your Tallinn or Harjumaa apartment, it's worth considering siphon and trap choices before ordering furniture, as cabinet dimensions often dictate which siphon type is even suitable.
This article provides practical criteria that will help you make an informed decision or at least communicate knowledgeably with your installer.
Why Is Choosing the Right Siphon Important for an Apartment?
The primary function of a siphon, or water seal, is to prevent sewage gases from entering your living space while allowing wastewater to drain freely. An incorrect type, size, or installation height can lead to three types of problems: slow drainage, blockages, and unpleasant odours.
In an apartment, another factor comes into play – the shared riser. When many apartment drains discharge into a single pipe simultaneously, a momentary negative pressure can occur, emptying the water seal. Therefore, when selecting a siphon for an apartment, it's advisable to favour solutions with a deeper water seal and, if necessary, consider a variant with a vacuum valve.
What Are the Main Siphon Types and When to Use Them?
Several main siphon types 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 kitchen and hand wash basins. Its advantage lies in easy dismantling and cleaning – simply unscrew the bottle-shaped part. The water seal 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 chrome-plated brass or white plastic (PP)
Shallow Siphon (Low-Profile Siphon)
The shallow siphon is designed for low-profile 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 seal volume, requiring more frequent monitoring to prevent water evaporation (e.g., in a rarely used bathroom).
- The only viable solution for very low cabinets or wall-mounted basins
- Smaller water seal dries out faster during long periods of disuse
- Slightly more challenging to clean than a bottle siphon
Dry Siphon and Vacuum Valve (Mechanical Water Seal)
A dry siphon uses a membrane or valve instead of water, opening only when water flows through and otherwise sealing completely. This solves the evaporation problem and is well-suited for rarely used drains, such as guest WCs, summer cottage basins, or infrequently used floor drains.
In apartment buildings, a dry siphon or a solution supplemented with a vacuum valve is a sensible choice where you want to guarantee protection against sewer odours, even if the water seal might empty due to a vacuum.
- Does not dry out or empty due to vacuum
- Suitable for seasonal use (holiday home, guest room)
- Membrane needs occasional inspection as it may wear over time
Shower Trap vs. Floor Drain — What's the Difference?
For bathroom floor drainage, you need to choose whether to install a linear (channel-type) shower trap, a round floor drain, or a shallow trap hidden beneath the shower enclosure.
- Always ensure that the water seal depth of the trap meets manufacturer and regulatory requirements (generally at least 50 mm)
- Prefer traps where the water seal part can be removed for cleaning without tools
- If the bathroom is used infrequently, consider a trap with a dry water seal
Classic Floor Drain
A round or square floor drain suits most bathrooms and is the most common choice in apartments. Its water seal is usually removable and cleanable from above, without damaging the floor.
Linear Shower Drain
A linear drain is typically placed along the edge of the shower enclosure and allows for floor gradient in only one direction, simplifying tiling. In an apartment, before making a choice, check if the existing floor slab and drain pipe location allow for sufficient slope – otherwise, water will stand around the drain.
How to Account for Siphon Height with Low Cabinets?
Before ordering cabinet furniture, always measure the available space between the basin's drain opening and the cabinet base. This is the most common mistake leading to the need for a siphon replacement later.
If furniture is already in place and space is limited, a shallow siphon is often the only viable solution. However, if you're planning a renovation, it's wise to allow sufficient clearance when choosing cabinets – this gives you the freedom to select a higher quality and more maintenance-friendly bottle siphon.
- Measure the free height from the drain opening to the cabinet base before ordering furniture
- For a bottle siphon, ideally leave at least 15–18 cm of free space
- A shallow siphon usually requires 6–10 cm, but exact dimensions vary by manufacturer
- Corner basins and wall-mounted basins often require a special corner siphon
Which Drain Opening Diameter Suits Which Appliance?
The diameter of the siphon and drain pipe must match the volume of water and how quickly it drains from the appliance. An incorrectly sized siphon is a frequent cause of blockages and slow drainage in apartments.
- 32 mm — hand wash basin, smaller sink
- 40 mm — kitchen sink, baths, shower cabins, washing machine and dishwasher
- 50 mm — floor drains and larger basins
- 50–110 mm — WC pan connection according to the sewage riser diameter
Chrome-Plated Brass or White Plastic (PP) — Which Material to Choose?
Siphons are primarily made from two materials: impact-resistant polypropylene (PP) and chrome-plated brass. Both have their advantages, and in an apartment context, the choice mainly depends 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 critical.
Chrome-Plated Brass
Brass siphons are more aesthetic and typically used where the siphon remains visible, such as under a designer basin without a cabinet. They are more resistant to mechanical stress but 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 spillage onto the floor in case of appliance malfunction. This requires a special siphon with an overflow pipe, featuring a separate connector for the overflow hose.
Washing machine and dishwasher drains must not go directly into the sewage system but must be connected to the siphon via a special connector (a 'machine connector') with its own non-return valve. This prevents sewage water from flowing back into the appliance and avoids odour generation.
- Ensure the siphon has the designated connector for the washing machine or dishwasher hose
- For baths with an overflow, only use a siphon with an overflow connector
- Do not connect two high-volume appliances (e.g., washing machine and dishwasher) to the same connector simultaneously
Why Do Odours or Noise Occur from Siphons with Insufficient Water Seal Depth?
If the siphon's water seal depth is too shallow, or if the water evaporates from it, a direct connection forms between the room air and the sewage pipe. This results in a characteristic sewer odour, typically stronger in the mornings when water has partially evaporated overnight.
Noise, such as gurgling or slurping sounds in the drainpipe, may indicate that the siphon or riser ventilation is not functioning correctly, and the water flow creates negative pressure, causing the water seal to vibrate. In such cases, a siphon supplemented with a dry water seal or an inspection of the existing ventilation system usually helps in an apartment.
- For infrequently used basins, choose a siphon with a dry water seal
- If odours occur regularly in a specific location, check the water seal depth and water level
- Recurring gurgling likely indicates a riser ventilation problem, not the siphon itself
What Else to Consider in an Apartment Building?
An apartment building's sewage system differs from a detached house mainly because many flats share a common riser. This means your siphon's performance is 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, they may have sediment build-up, reducing flow capacity and creating larger-than-normal pressure fluctuations. In such cases, it makes sense to choose a siphon with a slightly deeper water seal and, if necessary, discuss the riser's condition with the apartment association.
- In renovated apartment buildings, the ventilation riser may be missing or blocked, increasing the risk of vacuum
- During renovation, it's worth checking the condition of old pipes simultaneously – read more about old cast iron pipes
- If drainage is slow or repeated blockages occur, the siphon may not be to blame, but the riser itself
What to Consider When Choosing a WC Pan Drain Connection in an Apartment?
The WC pan connection to the sewage riser differs from a standard siphon because most WC pans have a built-in water seal within the pan's design, so a separate siphon is usually not used. However, correct selection of the pan connector or sealing sleeve, which connects the pan's outlet to the drainpipe, is crucial.
In an apartment building, where pipe diameters and locations may differ from manufacturer standards, a pan connector of suitable length and angle must be chosen – a too short or incorrectly angled connector 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 worth checking the location of the floor or wall drain and ensuring that the new pan's dimensions are compatible with the existing connection point; otherwise, adapter pieces or repositioning the connection may be necessary.
- Before buying a new WC pan, check the location and type of the existing drain connection (to the floor or wall)
- Use a high-quality, flexible pan connector that tolerates slight shifts without leaking
- Avoid over-tightening when securing the pan, as this can compress the connector and restrict drainage
How to Choose a Siphon When Renovating a Bathroom and Kitchen Simultaneously?
During a major renovation where the bath, basin, and kitchen cabinets are all being replaced, it's wise 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's sensible to create a list of all drainage points, including their diameter, cabinet height, and frequency of use, and then select the appropriate siphon type for each location based on this information, rather than randomly choosing 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 a siphon yourself, ensure before purchasing that the new product's connecting parts are precisely compatible with the existing pipework, as manufacturers' dimensions can vary slightly even for products with the same name.
If the renovation also involves updating the pipework itself, it's worth considering the suitability of the riser's ventilation and diameter for the load of new appliances, especially if, for example, an additional bathroom or utility room is being added that wasn't previously in the building.
What Are the Signs That Your Apartment's Existing Siphon Needs Replacing?
Even if a siphon isn't visibly leaking, several signs can 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 needed tightening, indicating thread wear
- Drainage has become slower, even though cleaning hasn't solved the problem
- A regular gurgling or slurping sound comes from the siphon
- There's a faint but persistent damp smell in the cabinet, even if no visible water is present
What Practical Advice Should You Follow When Installing a Siphon?
Even choosing the right siphon doesn't guarantee success if the installation is sloppy. Some simple rules can help prevent future leaks and blockages.
- Always use the supplied gaskets, not silicone as a sealant – silicone makes later disassembly difficult
- Do not over-tighten plastic fittings, as this can strip the threads
- After installation, check for leaks with running water for at least 15–20 minutes
- Leave access below the siphon so that future cleaning or replacement is possible without damaging furniture
Does Siphon Type Affect Drain Eco-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 agents are used. A bottle siphon with an easily openable, removable bottom allows for regular mechanical removal of accumulated hair, food scraps, and grease, without chemical cleaners, which is a more environmentally friendly solution and kinder to pipe seals.
Shallow siphons and narrower diameter solutions often have a smaller internal volume, meaning debris accumulates to a critical level more quickly, requiring 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 part replacement, and generates fewer waste products from old, broken parts. If you doubt 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 limiting the check to only the visible part.
Summary: How to Make the Final Choice?
Choosing a siphon for an apartment boils down to three questions: how much space is under the furniture, what is the water volume of the appliance draining, and how often is that drain used. A shallow siphon suits narrow cabinets, a dry siphon for rarely used basins, and a standard bottle siphon for typical kitchen or bathroom basins.
If the choice seems complex, or if your apartment building experiences recurring problems with odours, noise, or slow drainage, it's advisable to engage a professional to assess the condition of both the siphon and the wider drainage system.