London's kitchen drains were not built for modern cooking. Most of the city's older homes have 100mm clay or cast-iron pipes. They were laid when households cooked with less fat, had no dishwashers and put nothing down the sink that dissolved in cold water. This mismatch explains why kitchen blockages cause so many drain emergencies across the capital.
It also explains why Thames Water spends so much clearing fatbergs from the public sewer. The good news is that prevention is simple, because five everyday substances cause most avoidable kitchen blockages. Here is each one, with a better way to dispose of it.
1. Cooking Fats, Oils and Grease
Fat does the most damage of all, because it sets hard. It leaves the pan as a liquid, but it cools fast inside the cold underground pipe. Within a few metres it sets on the pipe wall.
Each pour adds a layer and narrows the bore, so the pipe is soon half blocked. Then wet wipes, food scraps and hair catch on the fat, so the blockage becomes total.
The same process builds fatbergs in the public sewer. The 2017 Whitechapel fatberg weighed 130 tonnes. Thames Water needed a specialist team to remove it.
That case is only the visible end of a bigger problem, because fat builds up in sewers across London. For more detail, see our overview of why London drains block so often.
The fix is simple, since it needs no tools. Pour cooled fat into an empty jar or carton and let it set. Then put it in your household waste.
Wipe greasy pans with kitchen paper before you wash them, because this keeps fat out of the pipe. Once years of fat have damaged a drain, high-pressure jetting will clear the blockage. It will not restore the pipe's original bore, so prevention is far cheaper than cure.
2. Coffee Grounds
Coffee grounds look harmless, since they are small and seem to wash away. In practice they cause many kitchen blockages in London. They never dissolve.
They settle wherever the flow slows, such as the trap, a flat section or a bend, because water cannot carry them on. There they pack into a dense sediment that water cannot shift.
London terraces and converted flats often have long, flat kitchen pipes. Many kitchens have moved or grown over the years, so the falls are shallow, while the pipes stay narrow. Grounds settle in the first metre or two and mix with fat. The result is a stubborn blockage, and we see it often in Hackney, Islington and Camden.
Put grounds in a food waste caddy or compost bin, since they make good compost. They make excellent compost, and they break down quickly. If your borough offers food waste collection, use it.
Otherwise, the grounds can go in general waste. Our kitchen drain blockages page explains how we clear a blockage that grounds have already caused.
3. Rice, Pasta and Other Starchy Foods
Rice and pasta keep absorbing water after they enter the drain, so they swell. A little leftover rice can swell to several times its size in the trap. It forms a soft paste that blocks the flow. The starchy cooking water adds a glue-like film, and the film catches everything that follows.
Bread and flour behave the same way, although they cause less fuss at first. Old pipes are rough inside, from rust in cast iron or limescale in clay, so starch finds plenty to stick to. Shallow falls also give the starch time to settle before it reaches the stack. These blockages respond poorly to chemical cleaners, so they often need jetting.
Scrape rice, pasta, bread and pastry into a food waste caddy, compost bin or general waste, while you wash up. Use a sink strainer to catch loose grains and crumbs while you wash up. A strainer plus careful scraping stops most starch blockages, and it costs almost nothing.
4. Eggshells, Bones, Peelings and Other Solids
Solid scraps are the wrong shape for a kitchen drain, because they cannot bend round corners. Eggshells break into sharp pieces that catch fat and starch. Bones, fruit stones and large peelings settle at the trap and block the flow on their own. Stringy vegetables such as celery and leek tops tangle into a mat that water cannot pass.
Waste disposal units do not solve this, because they make it worse. A unit grinds scraps into slurry that travels further down the pipe before it settles. Blockages then form deeper in the drain, where they are harder to clear.
Ground food also bonds with fat, since both are sticky, to make a dense, cement-like deposit. Many of the worst kitchen blockages we attend are in homes with a disposal unit.
Use a food waste caddy instead, because it keeps solids out of the pipe. Empty it into your borough's food waste collection or a garden compost bin. If you have a recurring kitchen blockage, check what goes down the sink before you pay for another clearance.
5. Wet Wipes, Cotton Wool, Sanitary Products and Anything Labelled "Flushable"
Wet wipes are a bathroom problem, yet they affect the kitchen too. They accumulate in the main drain, and that blocks every appliance in the house. The label "flushable" misleads people.
A wipe passes the toilet trap, yet it does not break down like paper. It piles up at the first bend or restriction.
When wipes meet kitchen fat in the drain, they form the material that makes fatbergs, because both are sticky. Thames Water names wipes and fat as leading causes of sewer blockages in London. Cotton buds, dental floss, sanitary products, nappies and paper towels behave the same way. None of them break down in cold water, so they all collect downstream.
The rule is simple, since it has only one line. Only pee, poo and toilet paper belong in a toilet. Everything else goes in a bin, including products labelled "flushable". Our piece on the October 2011 transfer of private sewers to Thames Water explains who pays when a blockage does occur.
London Kitchen Drain Care: Why Prevention Matters More Here
London's drains are older and narrower than those in many UK cities, although they still serve millions of homes. Most home pipework is glazed clay or cast iron. Sir Joseph Bazalgette designed the sewer system in the 1860s, and builders extended it over the next century.
Home drains are typically 100mm wide. That suited Victorian water use, yet it struggles with modern dishwashers, washing machines and heavy cooking. Greater London also sits on London Clay, which swells and shrinks and cracks joints in old drains.
As a result, London kitchen drains cope badly with things that would cause a minor problem elsewhere. A little fat might clear in modern plastic pipe with a steep fall. In a century-old clay pipe with a shallow fall and a rough interior, it sets hard. Therefore these five rules are necessary maintenance, not optional advice.
Local conditions differ, however. Inner boroughs with the densest Victorian housing, such as Hackney, Islington, Camden, Westminster and Kensington, have the oldest drains. They gain most from strict kitchen habits.
Outer boroughs like Bromley and Greenwich have a mix of pipe ages, while newer post-war pipes tolerate more. Treat the five rules as absolute in any home built before 1900. A history of repeat kitchen blockages calls for a CCTV survey to check for damage.
A CCTV inspection is the only reliable way to know your drain's condition, because it shows what sits inside. The recording shows how much fat, scale or root growth has built up. Our CCTV survey cost page covers pricing. For an active blockage now, request a quote online via our contact form.
Frequently Asked Questions
Can I pour boiling water down the sink to clear cooking fat?
Boiling water melts the fat at the trap, but the fat sets again as it cools further down, because the pipe is cold. It can form a worse blockage where it is harder to reach. At best, this is a temporary fix. Catching fat before it enters the drain is the only reliable approach.
Are biological drain treatments safe to use regularly?
Enzyme-based treatments are much safer than caustic cleaners, particularly on old clay and cast-iron pipes. They work slowly by digesting organic deposits, so use them as monthly upkeep. They will not clear an existing blockage. They also do nothing for wipes or coffee grounds.
Does using a dishwasher reduce the risk of kitchen drain blockages?
A dishwasher filters food debris before it reaches the drain, while it uses less water than hand washing. Homes with dishwashers often have cleaner kitchen pipes, provided you empty the filter often. Scrape plates before loading. Together with the five rules, a dishwasher is generally good for your drains.
How often should I clean my kitchen sink trap?
For most homes, clean the trap every few months, since fat builds up slowly. This removes fat, debris and limescale before they slow the drain. Homes that cook often, or older homes with shallow falls, benefit from cleaning more often. The job takes minutes and prevents most blockages at the fixture.
What does it cost to clear a fat-based kitchen blockage in London?
The cost depends on access and whether jetting is needed. Fat that has built up over several years often needs high-pressure jetting. We may also run a CCTV check to confirm the pipe is sound afterwards. Prevention costs nothing, and it saves both the call-out and long-term damage.
Because every property is different, start with our guides to blocked drains and commercial cctv drain surveys advice. We also cover blocked drains in Croydon and blocked drains in Ealing, so you can see how the work runs near you.
