Blocked drain or sewer: the cause, unblocking it yourself and who does it (and pays)

A blocked drain almost always comes at a bad moment: the kitchen sink is full of washing-up water, the toilet no longer flushes or water bubbles up into the shower tray while someone upstairs is running the washing machine. At that point you want to know quickly whether you can solve this yourself, or whether a plumber or drain unblocking company needs to come, and who pays for it. In this article you can read how to tell where the blockage is, what the most common causes are, what you can safely try yourself, what a tradesperson does, how responsibility is divided between you, the landlord and the municipality, and how to avoid calling a rogue emergency service in a panic.

Where is the blockage? Symptoms by location

The first question is always: is it one drain, or several at once? That usually tells you straight away whether the problem is close to the fixture or further away in the pipe.

One drain is slow or not draining at all

• Kitchen sink. The water drains away slowly, a thin layer is left standing or there is a musty smell. The blockage is usually in the trap (the bend under the sink) or just behind it, caused by grease and food scraps.
• Shower or bath. The water stays on the floor or in the bath. Hair mixed with soap residue often forms a plug just below the drain here.
• Washbasin. Hair, toothpaste and soap collect in the trap and around the plug.
• Toilet. When you flush, the water rises almost to the rim and then drains away very slowly. The blockage is often in the bowl itself or in the first section of the drain, for example because of too much paper or something that does not belong there.

If only one fixture is blocked and the other drains in the house are working normally, the problem is almost always in the first section of pipe at that fixture. That is the situation in which trying it yourself makes sense.

Several drains at once: probably the main sewer pipe

If several drains are not working properly at the same time, the blockage is probably further along, in the pipe into which all the drains run or in the connection to the public sewer. Signs of this are:

• the toilet gurgles or the water in the bowl moves when you use the sink or shower;
• water from a drain higher up comes up into a drain lower down, for example into the shower or toilet on the ground floor when someone is showering upstairs;
• there is water in the inspection chamber (ontstoppingsput) or water is coming up from a drain in the garden or the basement;
• there is a persistent sewer smell in the house or garden.

The municipality of The Hague names exactly these signs, more than one drain not working or waste water from upstairs coming up downstairs, as the hallmark of a major blockage for which you call a plumber, or the owner if you are a tenant. With a blockage like this, a plunger or drain unblocker from the supermarket usually does not help, because the plug is too far away.

The most common causes

• Grease and oil. Frying fat, cooking fat and gravy are still liquid when warm, but solidify in the cold pipe. Together with food scraps and soap, they form a hard layer that makes the pipe narrower and narrower.
• Hair and soap residue. The classic cause in showers and washbasins.
• Wet wipes and other waste in the toilet. Wet wipes do not belong in the toilet, even if the packaging says they can be flushed. According to Milieu Centraal (the Dutch independent information centre on energy and the environment), most wipes are solid waste; only moist toilet paper with the logo of a toilet bowl may be flushed. Stichting RIONED (the Dutch sewerage knowledge foundation) concludes that wet wipes are almost never suitable for flushing and cause blockages in the sewer system and in house connections. The same applies to sanitary towels, tampons, cotton buds and kitchen roll.
• Tree roots. Roots seek out moisture and grow into the sewer pipe through small gaps and leaking joints, especially in older concrete or vitrified clay pipes. Dirt then gets caught on them.
• Subsidence. On soft ground, a pipe can sink over the years. This creates a low point (a "dip") where water and dirt collect, or a displaced joint where the flow is hampered.
• Limescale and dirt build-up. Especially with hard water, soap residue together with limescale can form deposits in the trap and the drain. Usually this plays a secondary role alongside hair and grease, but it can gradually reduce the bore of the pipe.
• Too shallow a fall or an incorrectly installed drain. After a renovation, a new drain may be too flat or have too many bends. Then the blockage keeps coming back.

What can you safely try yourself?

With a single blocked drain, you can usually try it yourself first. Always start mechanically, so with tools and not with chemicals.

1. The plunger. Place the rubber plunger over the drain, make sure there is a little water above it and push up and down forcefully a number of times. With a washbasin or sink, cover the overflow with a wet cloth, otherwise the pressure escapes there. There is a separate toilet plunger with a longer flange that fits into the outlet of the bowl.
2. Removing the trap. Under the sink or washbasin there is a trap that you can unscrew by hand. Put a bucket underneath first, undo the nuts and clean the bend. When refitting it, check that the rubber rings are seated properly, otherwise the trap will leak.
3. A drain snake. A flexible metal spiral that you twist into the drain to pull out or break up a plug. The municipality of The Hague names the drain snake as a way to clear a small blockage in the house yourself. Work carefully with a toilet, so that you do not damage the porcelain.
4. Hot water. With a light grease blockage, hot tap water can help to loosen the grease. Preferably do not pour boiling water down the drain: many drains are made of PVC, which is not designed for large amounts of boiling water and can therefore deform or start leaking at the joints, and a sudden change in temperature can damage the porcelain of a toilet.

Be careful with chemical drain unblockers

Liquid drain unblockers and unblocking granules often contain corrosive substances such as sodium hydroxide (caustic soda) or strong acids such as sulphuric acid. The municipality of The Hague advises against using chemicals if possible, because they damage the sewer. Milieu Centraal also advises against chemical drain unblockers. They are dangerous to skin and eyes, put a burden on waste water and work poorly if the blockage is further away, because the product then becomes diluted in the water standing in the pipe. If you do use a product, follow the instructions, wear gloves and goggles and ventilate well. Important:

• Never mix different products. Chlorine-based products together with an acid, such as a descaler or acidic drain unblocker, can produce toxic chlorine fumes. Note: some drain unblockers also contain chlorine themselves.
• Do not use another drain unblocker if there is already a product in the drain, and do not use a plunger afterwards either: the corrosive water can then splash up.
• Tell the tradesperson if you have already used a chemical product, so that they know what they are working with.

If the plunger, trap and snake do not work within a reasonable time, stop. Carrying on by pushing harder or using more product rarely makes things better and can damage pipes or joints.

When should you call a tradesperson?

• Several drains are blocked at the same time, or water comes up into a drain lower down.
• The blockage keeps coming back, even after you have cleaned the trap.
• There is water in the inspection chamber or water is coming up from a drain outside.
• You smell sewage persistently, even without a visible blockage.
• The toilet stays blocked after you have tried a toilet plunger.
• There is water in the crawl space, or you suspect a leaking or broken pipe.

A plumber clears blockages in and around the house. For the sewer outside, the pipe from your home to the street, a specialist drain unblocking or sewer service company often has the heavier equipment. If you are unsure which tradesperson goes with which problem, read Plumber, installer or central heating engineer: who do you call for what?. If it is about water getting in somewhere, Leaks: which tradesperson should you call? will help you further.

What does the plumber or drain unblocking company do?

• Mechanical unblocking. An electric or hand-operated drain snake (spiral) is used to pull out or break through the plug. This is the standard approach for drains inside the house.
• High-pressure jetting. A hose with a nozzle sprays water at high pressure through the pipe and flushes away grease, sludge and loose roots. This is suitable for longer sections of sewer and for pipes that are fouled along their entire length.
• Camera inspection. A camera on a cable goes into the pipe. This lets the tradesperson see where the blockage is, whether roots are growing into the pipe, whether the pipe has subsided or broken, and at which point. With blockages that keep coming back, this is often the only way to find the real cause. Note: according to the municipality of The Hague, the municipality does not reimburse a video inspection, not even if the blockage ultimately turns out to be on municipal land. Other municipalities may have their own rules on this.
• Relining or replacement. If the pipe is damaged, it can sometimes be repaired from the inside by relining: a resin-impregnated liner is inserted into the existing pipe, where it cures and forms a new inner pipe, without any digging. If the pipe has subsided badly or collapsed, the section has to be dug up and replaced.

Ask the tradesperson to explain what they found and, in the case of a camera inspection, for the footage or a short report. You will need this if the municipality, the landlord or the insurer later asks where the blockage was and what caused it.

Who is responsible: you or the municipality?

The sewer of your home consists of two parts. The part on your own land, from the drains in the house to roughly the property boundary, belongs to the owner of the home. The part in public land, from the property boundary up to and including the main sewer in the street, falls under the municipality. The municipality of Neder-Betuwe explains it like this: the municipality manages the main sewer and the house connections up to the property boundary, often the boundary between the pavement and the front garden. The exact boundary differs per municipality; Utrecht, for example, places the homeowner's responsibility up to half a metre beyond the plot boundary. So always check the website of your own municipality.

The inspection chamber as a gauge

A properly installed house sewer has an inspection chamber or rodding point (ontstoppingsput or ontstoppingsstuk) on your own land, close to the property boundary: a piece of pipe with a cover, usually around thirty to seventy centimetres below ground according to the municipality of Neder-Betuwe. You can use it to work out which side the blockage is on:

• If the chamber is (almost) dry, the blockage is on your own land, between the house and the chamber. In that case you, as the owner, are responsible.
• If the chamber is full of water, the blockage is further towards the street, in the municipal part. In that case contact the municipality before you let a company carry on working yourself.

If you do not know where the chamber is, ask the municipality; sometimes there are drawings. Especially in older homes, an inspection chamber is sometimes missing. Municipalities differ in what they reimburse: according to the municipality of Neder-Betuwe, digging up the rodding point and locating the fault are at the owner's expense, even if the blockage ultimately turns out to be on the municipality's side.

Do not let a company work on the public sewer

If the blockage is in the municipal part, a plumber may not solve it themselves, according to the municipalities of The Hague and Utrecht. You report the blockage to the municipality, which has it cleared and bears the costs of the municipal part. If you nevertheless let a company unblock the public sewer without consultation, you run the risk of paying that bill yourself: the municipality of Neder-Betuwe, for example, only reimburses such costs if the municipality itself gave the instruction in advance. Conversely, the municipality can charge you costs if, after your report, the blockage turns out to be on your own land after all; Utrecht charges a fixed amount for this. With a major blockage, the best order is therefore: look in the inspection chamber, if there is water in the chamber call the municipality first, and if the chamber is dry engage a tradesperson yourself.

Renting? Then things are different

If you are a tenant, first report a blockage to your landlord or housing association. Under the Besluit kleine herstellingen (the Dutch Minor Repairs Decree), keeping the indoor drainage clean and, if necessary, unblocking it up to the connection point on the municipal or main sewer is the tenant's responsibility, insofar as that drainage is accessible to the tenant. An ordinary blockage in the sink or toilet is therefore usually a job for the tenant. If the cause lies in a defect in the pipe itself, such as root ingrowth, subsidence or a broken pipe, that is a defect for which the landlord is responsible. Many housing associations also have a service subscription that covers unblocking; check your tenancy agreement.

Does the insurance pay towards it?

Buildings or contents insurance often covers the water damage caused by a blockage, for example if a toilet or drain overflows and the floor or ceiling gets wet. The unblocking itself, and tracing or repairing a sewer that has subsided or been damaged by roots, is usually not covered by the standard policy. Check your policy conditions and, if in doubt, call your insurer first; it sometimes has its own assistance service too. You can read more about what buildings insurance does and does not cover in Renovating and insurance: buildings, CAR and liability.

Watch out for rogue drain unblocking services

A blocked sewer is exactly the situation in which rogue emergency services strike. In 2021 the Autoriteit Consument & Markt (ACM, the Dutch Authority for Consumers and Markets) took action against lead-generation companies that misled customers searching for a locksmith or another emergency service, with sewer unblocking expressly mentioned. The ACM described websites with a town or province name in the domain name that suggest a local business, while the customer often did not know which company would eventually turn up and what it would cost. In practice, a much higher bill then sometimes follows on the spot, which has to be paid immediately. This is how to protect yourself:

• Ask in advance what it costs: call-out charge, the hourly rate or a fixed price, and any surcharges for evenings or weekends. Have that confirmed by email or text message.
• Ask who will carry out the job, and check the company name and the KvK (Chamber of Commerce) number.
• Do not sign anything blank and do not let yourself be pressured into approving a major repair or replacement straight away. For a major intervention, ask for time to think it over or a second opinion.
• Do not pay a large amount on the spot by card or in cash because it "has to be done now". Ask for an itemised invoice with a KvK and VAT number.
• If there is water in the inspection chamber, call the municipality first, before you engage a company.

You can read more signs of a reliable and a rogue tradesperson in How to recognise a reliable plumber.

Preventing blockages

• No grease down the sink. Let frying and cooking fat cool down and hand it in, or put it in a sealed container in the residual waste. Wipe the grease out of pans with kitchen roll before you wash up.
• Only pee, poo and toilet paper in the toilet. Wet wipes, sanitary towels, cotton buds and kitchen roll belong in the bin.
• A hair catcher in the shower and a strainer in the sink keep hair and food scraps out.
• Clean the trap and the shower drain regularly, for example as part of your regular maintenance calendar.
• Do not plant trees and large shrubs right above the sewer, and know where your sewer pipe and inspection chamber are.
• During a renovation, have the drains installed with sufficient fall, with as few sharp bends as possible, and have an inspection chamber fitted if there is not one yet.

Not managing it yourself, or is the blockage further along the pipe? Post your job on VerbouwPro and get in touch with a plumber near you.