Why does the sink keep getting blocked?
A sink that keeps getting blocked almost always has grease stuck inside the pipe. Every time you wash up, that layer traps food scraps and soap; the plunger clears the blockage temporarily, but the grease is still there and the blockage returns within a few weeks.
It’s a problem specific to the kitchen. The sink ends up with everything that doesn’t go down any other drain in the house: oil, food scraps, coffee grounds and water containing dishwasher detergent. That’s why it gets blocked differently to a washbasin or a shower, and that’s why the solution is different too.
In this guide, you’ll find out what causes your sink to become blocked repeatedly, how to locate the blockage, what you can do yourself, and when you need to have your pipes pressure-cleaned to prevent it from happening again.
Reasons why a sink keeps getting blocked
When a sink blockage keeps recurring, it’s not just a single blockage: something builds up every time you use it. Here are the six most common causes, listed from most to least frequent.
1. Grease and oil stuck to the pipe
It’s the main culprit in any kitchen. The oil flows freely with the hot water, but as it cools it solidifies and sticks to the inside walls of the pipe. Food scraps then get stuck to this layer, and the pipe becomes a little narrower with every wash-up.
That’s why the suction cup only works for a few days: it creates a hole in the fat, but doesn’t remove it.
2. Food scraps and coffee grounds
Rice, pasta, fruit peel, eggshells and coffee grounds do not dissolve. They settle in the siphon and in the bends of the pipework and, when mixed with grease, form a compact paste. If you’d like to know what other types of waste end up causing blockages, we explain this in the section on materials that commonly cause blockages in pipes.
3. Soap and limescale in the trap
Soap and detergent residues combine with the limescale in the water to form a build-up in the siphon and the drainpipe. The sink starts to drain more and more slowly, even if you don’t pour food scraps down it. If you live in the Marina Alta, you’ll want to read about how hard water affects your pipes.
4. A dirty or incorrectly fitted siphon
The trap is the curved or U-shaped section beneath the sink, and this is where most dirt accumulates. If, in addition, it is fitted incorrectly, has an adverse slope or the pipe leading out of it is too narrow, waste will always remain in the same spot. Basic Document HS 5 of the Technical Building Code sets out the requirements for diameters, gradients and water seals in drainage systems.
5. Dishwasher or washing machine connected to the sink
If your dishwasher or washing machine drains into the sink, they send a large amount of water through all at once, along with grease and detergent residue, which accelerates the build-up in the pipework. If, when you switch them on, you notice water rising up through the sink, this is a backflow: we’ll explain the reasons why water rises up through the drain.
6. The problem goes beyond the kitchen
If the sink shares a pipe with other appliances, the blockage may be located beyond the joint. In a flat, grease from several kitchens accumulates in the building’s blocked downpipe; in a house, it usually gets stuck in the first blocked trap. And if the blockage returns even after it has been thoroughly cleared, there may be a crushed section of pipe or a misaligned joint – something common in old installations, as we explain in our guide on how to prevent recurring blockages in old buildings. In that case, it is advisable to rule out a broken drainpipe.
How to find out where the blockage is in your sink
Take a look at how the sink behaves: it tells you quite a lot about where the plug is.
| What you notice | Most likely cause | What’s the problem? |
|---|---|---|
| The water drains slowly and smells of grease or food | Grease and food scraps | Sink trap and pipework |
| You’ll notice an improvement as soon as you clean the trap | A siphon that is dirty or clogged with soap and limescale | Siphon |
| Water rises in the sink when the dishwasher is turned on | Partial obstruction on the shared section | Standard kitchen pipework |
| The sink and other drains get blocked at the same time | Common section, downpipe or manhole | Housing or building network |
| It’s blocked up again just a few days after it was unblocked | Grease build-up or damaged pipework | Inside the pipe |
How to unblock a sink, step by step
If the blockage is in the trap or just beyond it, you can sort it out yourself in four steps. Follow them in this order, from least to most invasive.
Step 1: Empty the bin and do not use the electrical appliances
Do not run the dishwasher or washing machine whilst the sink is blocked: each flush raises the water level. Use a container to remove any water from the sink.
Step 2: Clean the trap
Place a bucket underneath, unscrew the trap and empty its contents. Wash it with hot soapy water, check that the seals are secure and reassemble it, tightening it firmly. In many sinks, this step is enough to clear the blockage.
Step 3: Use the suction cup to cover the overflow
If the sink has an overflow or two basins, plug the other hole with a damp cloth so that the pressure doesn’t escape. Place the plunger over the drain with a little water in it, and push and pull firmly several times.
Step 4: warm soapy water and, if necessary, a sponge
A squirt of washing-up liquid followed by hot water will break down fresh grease. If the blockage is beyond the trap, insert a manual drain snake into the trap outlet, twist it as you push it in, and remove whatever comes out.
What to avoid
Do not use caustic soda or chemical drain unblockers, and never mix different products. We explain why in our guide to common mistakes when trying to unblock pipes yourself. If you’re looking for a guide to any drain in the house, see our guide on how to clean drain pipes.
If, after following these steps, the sink becomes blocked again within a few days or weeks, the problem is no longer with the trap: there is grease build-up in the pipe or a blockage in a shared section, and household tools cannot reach that far.
When your sink needs more than just unblocking
If the sink keeps getting blocked even though you’ve cleaned the trap, the grease has already spread through the pipe. Unblocking it only clears a section; to stop it happening again, you need to clean the entire pipe. These signs indicate this:
- It gets blocked again just a few days or weeks after it has been unblocked.
- The water takes a long time to drain, even though the trap is clean.
- There’s a lingering smell of grease in the kitchen.
- The sink and other drains in the house become blocked at the same time.
If you have concerns about another drain in the house, find out when you should call a drain clearance professional.
At Limpiezas Domingo e Hijos, we clear blockages and clean pipes using a tanker lorry and high-pressure water, which removes grease, sludge and limescale build-up from the pipes. If the blockage recurs even after cleaning, we recommend a CCTV inspection of your domestic pipes to see what is happening inside.
We operate in La Marina and La Safor. If it’s an emergency, please call 672 450 224.
Tips to stop your sink from getting blocked again
Almost all sink blockages start in the kitchen, so they can also be prevented there:
- Do not pour oil or grease down the drain. Let it cool, store it in a sealed bottle and take it to your local recycling centre or your local council’s oil collection point.
- Scrape plates and frying pans before washing up. Put grease and food scraps in the bin, not down the sink.
- Place a mesh strainer or small basket over the drain. It catches solids and can be emptied in a jiffy.
- Throw the coffee grounds, rice and peelings in the bin. They’re among the waste items that cause the most blockages.
- Clean the trap from time to time. That’s where the most dirt builds up.
The fat that goes down the sink doesn’t just stay in your pipes: it also ends up in the sewerage network. The Ministry for Ecological Transition devotes a section to the cleaning and maintenance of sewage pipes as part of the management of sewerage systems.
For tips that apply to all the drains in your home, see our guide to preventing blocked pipes.
Frequently asked questions about blocked sinks
Why does my sink get blocked every few weeks?
The most common cause is grease stuck to the inside walls of the pipe. Using a plunger or a spring-loaded drain cleaner clears a passage, but the layer of grease remains and continues to trap food debris. To prevent this from happening again, the entire cross-section of the pipe must be cleaned.
How do I know if the blockage is in the trap or further down the pipe?
If the sink works properly again once you’ve cleaned the trap, that was where the problem lay. If it’s still blocked, or if other drains are blocked as well, the blockage is in the pipework – in a shared section, in the downpipe or in a drain chamber.
Does pouring boiling water down the sink help to unblock it?
Hot soapy water helps to break down fresh grease, but it does not remove grease that has built up over months. Furthermore, boiling water can warp the joints in plastic pipes.
Where should I dispose of used oil so as not to block the sink?
Leave it to cool, pour it into a sealed bottle and take it to your local recycling centre or your local council’s oil collection point. Never pour it down the sink: as it cools, it solidifies and sticks to the inside of the pipes.
Do coffee grounds block the sink?
Yes. Coffee grounds do not dissolve: they settle in the siphon and in the bends of the pipework and, when mixed with grease, form a compact paste. It is best to throw them in the bin.
A sink that keeps getting blocked always needs a thorough clean
A sink that keeps getting blocked isn’t fixed by unblocking it every few weeks, but by removing the grease that builds up inside the pipe and changing a couple of habits in the kitchen. If cleaning the trap is no longer enough, the problem lies further down the pipe. And if you’re having the same problem with the toilet in the bathroom, read our article on toilets that keep getting blocked.
At Limpiezas Domingo e Hijos, we locate the source of the blockage and clear the pipe using a tanker lorry and high-pressure water to ensure the problem does not recur.
Call us on 672 450 224 or 966 447 070, or request a quote.