Pouring leftover grease down the kitchen sink might seem like a harmless habit. After all, it’s quick, easy, and the grease is usually still in liquid form. What harm could it really do? Many people believe that following it with a stream of hot water or a squirt of washing-up liquid will simply wash it away. But as drain specialists regularly warn, this approach can cause more harm than you might expect.
Unfortunately, that couldn’t be further from the truth.
What begins as a small act of convenience can lead to major plumbing issues inside your home, and even bigger problems beyond your property line. Grease, fat, and cooking oil may appear to vanish down the drain, but they can solidify within your pipes and form stubborn blockages over time. Worse still, when this waste enters the wider sewer network, it can contribute to enormous build-ups known as fatbergs: solid masses of congealed fat, oil, and waste that wreak havoc on public drainage systems.
In this article, we’ll explore exactly what happens when you pour grease down the drain, why it’s such a serious issue, and what you should be doing instead to protect your home and your community.
If you’re already dealing with slow drains or recurring blockages, DrainBoss — a trusted, family-run drainage company serving Sussex, Surrey, Hampshire, Kent, Brighton, and South London — provides expert support and emergency services, including CCTV surveys and professional grease removal.
The Myth of “Hot Water Fixes Everything”
A commonly held belief is that it’s perfectly acceptable to pour grease down the drain, so long as you follow it with hot water or washing-up liquid. The logic seems sound — hot water keeps the grease in a liquid state, and soap helps to break it down. Problem solved, right?
Unfortunately, that’s not how plumbing systems work.
The issue lies in what happens after the grease travels a short distance down your pipes. As it moves further from the warmth of your sink, the temperature quickly drops. This causes the grease to cool, solidify, and adhere to the inner walls of the pipes. Over time, more fat, food particles, and other debris collect on these sticky surfaces, gradually forming a stubborn blockage.
Washing-up liquid may temporarily emulsify grease — that is, break it into smaller droplets suspended in water — but this is not a permanent solution. Once the mixture moves beyond the emulsifying action of the soap, the fat can easily separate again and congeal.
In short, hot water and soap only delay the problem. They don’t eliminate it. And while you might not notice the consequences immediately, the build-up is still happening — out of sight, but not out of system.
Grease in Your Pipes: What Actually Happens
When you pour grease down the sink, it may look as though it simply disappears — but inside your plumbing system, quite the opposite is taking place. As the warm grease travels through your pipes, it begins to cool. Eventually, it reaches sections of the pipework that are colder and less frequently flushed with hot water. Here, the grease starts to solidify.
This solidified fat clings to the inside of your pipes, forming a thin but sticky coating. It doesn’t take long for this residue to build up layer by layer, especially if grease is poured down the sink regularly. Even cooking oils that remain liquid at room temperature — such as sunflower, vegetable, and olive oil — contribute to this build-up. They may not harden in the same way as animal fat, but they still cling to pipe walls and mix with food scraps, hair, soap scum, and other debris.
Over time, this greasy film turns into a thick sludge that reduces the diameter of your pipes. As the passage narrows, water drains more slowly, and the system becomes increasingly prone to full blockages. Worse still, grease attracts more particles — crumbs, coffee grounds, pasta, rice — which bind to the fatty layer and accelerate the formation of a clog.
This process doesn’t happen overnight, but by the time signs of a blockage appear — like slow drainage or unpleasant odours — the damage is already well under way.
From Kitchens to Catastrophes: The Fatberg Problem
While a single household pouring grease down the drain may not seem significant, the collective impact is staggering. When fats, oils, and grease (commonly known as FOG) enter the public sewer system from thousands of homes, restaurants, and businesses, they don’t simply wash away. Instead, they start to accumulate.
These substances congeal and bind with other materials found in sewers — such as wet wipes, sanitary products, and general waste — forming large, solid masses known as fatbergs. These fatbergs grow steadily, clinging to the walls and ceilings of sewer tunnels, and can eventually block entire sections of the network.
The United Kingdom has seen some notorious fatberg incidents in recent years. In 2019, a fatberg measuring 64 metres (210 feet) was discovered in Sidmouth, Devon. Made up of congealed fat, wet wipes, and other non-flushable waste, it took a dedicated team over eight weeks to remove it. Another infamous case occurred in Whitechapel, London, where a fatberg weighing 130 tonnes and stretching over 250 metres was found clogging the Victorian-era sewers beneath the city.
These blockages can cost millions of pounds to clear and pose serious public health risks. Sewer overflows caused by fatbergs can lead to raw sewage flooding streets, backing up into homes, and contaminating local waterways. For water authorities and councils, this means not only extensive labour and expense but also reputational and environmental damage.
What begins with a splash of oil down your kitchen sink can contribute to a nationwide infrastructure problem — one that affects everyone who depends on a clean, functioning drainage system.
Early Signs of Grease-Related Blockages
Grease build-up inside your drainage system rarely causes problems straight away. Instead, it accumulates gradually, often unnoticed — until the symptoms become too obvious to ignore. Catching these warning signs early can help you avoid more serious and costly plumbing issues later on.
Here are some of the most common signs that grease may be clogging your pipes:
- Slow Drainage: If water is taking noticeably longer to drain from your sink, bath, or shower, it could be due to a narrowing of the pipe caused by fatty deposits. Grease coats the inner walls of pipes and reduces the space for water to flow freely, leading to sluggish drainage.
- Gurgling or Bubbling Sounds: Unusual noises coming from your plugholes — particularly a gurgling or bubbling sound — often indicate that air is trapped in the pipes. This can happen when grease build-up restricts water flow and causes air pockets to form as the water struggles to pass through.
- Persistent Unpleasant Smells: One of the earliest and most noticeable signs is a bad smell coming from your sink or drain. As grease traps food particles and other debris, it begins to decompose inside your pipes, creating a foul odour that lingers around the kitchen or bathroom.
- Dampness or Moisture Under the Sink: A blockage can sometimes lead to leaks, especially if pressure builds up in the pipes. If you notice moisture, mould, or damp patches inside the cupboard beneath your sink, it could be a sign of a developing issue in the drainage system caused by internal build-up.
Recognising these symptoms and taking action early — whether through a professional inspection or a thorough clean — can help you prevent a full-blown blockage and the inconvenience that comes with it.
What to Do If You’ve Already Poured Grease Down the Drain
If you’ve already poured grease or cooking oil down the drain — whether knowingly or by accident — you’re certainly not alone. It’s a common mistake, but there are a few practical steps you can take to minimise the risk of long-term damage.
Start with a simple home remedy: boil a kettle of water and slowly pour it down the affected drain. Follow with a generous squirt of washing-up liquid, then flush again with hot water. This can help liquefy the grease and move it further along. However, it’s only a short-term fix — and the grease is still likely to re-solidify deeper in the pipe.
To help you understand what works and what doesn’t, here’s a quick reference guide:
| Method | Effectiveness | Notes |
| Boiling water + washing-up liquid | Temporary relief | May clear minor build-up near the sink but doesn’t remove deeper grease |
| Chemical drain cleaners | Not recommended | Can damage pipes and are often ineffective against grease-based clogs |
| DIY tools (e.g. wire hangers) | Risky and ineffective | Can push the blockage further or damage pipe linings |
| CCTV inspection by professionals | Highly effective | Identifies the exact location and nature of the blockage |
| High-pressure water jetting | Professional solution | Clears hardened grease safely and thoroughly |
If you’re noticing persistent issues like foul odours, slow drainage, or gurgling sounds, it’s best to leave it to trained drainage engineers. They use specialised tools and techniques that not only remove the blockage but also help prevent it from returning.
How Professionals Deal With Severe Grease Blockages
When a grease-related blockage becomes too stubborn for DIY solutions, it’s time to bring in professional drainage engineers. Unlike domestic remedies, professional services use specialised tools and techniques that are both more effective and safer for your plumbing system.
Here are some of the key methods used to clear severe grease build-ups:
- High-Pressure Water Jetting: This technique involves blasting water through the pipes at extremely high pressure. It’s powerful enough to cut through hardened grease, food waste, and other debris, flushing the blockage out of the system entirely. It’s fast, efficient, and environmentally friendly — relying only on water, not chemicals.
- CCTV Drain Inspection: Before any invasive work is carried out, professionals often use CCTV drain surveys to locate and assess the severity of the blockage. A small, waterproof camera is inserted into the pipe to provide real-time footage of the interior. This helps identify not only the exact location of the problem but also whether the pipe has suffered any structural damage.
- Mechanical Cleaning Tools: For particularly stubborn build-ups, professionals may use mechanical tools such as rotating drain rods or cutters. These are designed to physically scrape grease and debris from the pipe walls without damaging the pipe itself. In commercial or heavily blocked systems, robotic cutters may even be employed.
Attempting to fix a major blockage yourself can sometimes do more harm than good. Using makeshift tools like wire hangers or chemical cleaners may damage your pipework or push the blockage deeper into the system, making it harder to remove later.
Professional cleaning not only removes the current problem but also helps prevent future issues by restoring your pipes to their original diameter and flow capacity. It’s a long-term solution — not a temporary fix.
Grease Prevention Tips for Every Household
When it comes to protecting your drains, prevention is far more effective than cure. Avoiding grease-related blockages is simple, cost-effective, and saves you from future plumbing headaches. By adopting a few sensible habits and sharing them with everyone in your household, you can keep your drainage system flowing freely for years to come.
- Never Pour Grease Down the Sink: This is the golden rule. No matter how tempting it may be when tidying up after a meal, grease, fat, and cooking oil should never go down the drain — even in small amounts. Instead, let them cool and solidify, then dispose of them in the bin, or collect used oil in a sealed container for safe disposal.
- Use Boiling Water for Regular Maintenance: Pouring boiling water down your kitchen sink once or twice a week can help loosen and flush away small traces of grease before they accumulate. This simple habit can prevent minor build-ups from turning into major obstructions — but only when paired with proper grease disposal.
- Clean Filters, Sink Strainers, and Traps: Your sink’s filter or strainer plays a key role in catching food scraps that would otherwise contribute to clogs. Clean it regularly, along with the U-bend or trap beneath your sink. These areas are common gathering points for grease, debris, and bacteria.
- Educate Everyone at Home: Make sure all members of the household — including children and guests — understand what can and cannot go down the sink. Create a clear list of “do’s and don’ts” near the sink if needed. Items like oil, coffee grounds, eggshells, pasta, and rice are common offenders and should always be disposed of properly.
Taking small, proactive steps now can save you the inconvenience and cost of future drain emergencies. A little care in the kitchen goes a long way when it comes to keeping your pipes clear.
Conclusion
Pouring grease down the drain might seem like a minor household habit, but it carries consequences that extend far beyond your kitchen. What starts as a splash of oil can develop into a hardened blockage deep within your plumbing, or worse, contribute to sewer-wide fatbergs that threaten entire neighbourhoods. Understanding the impact of this everyday mistake is the first step towards prevention.
By disposing of grease properly, maintaining your drains regularly, and educating everyone in the home about what should and shouldn’t go down the sink, you’re not only protecting your property — you’re helping to preserve the health of your local drainage network.
For those times when a blockage does occur, it’s important to call on experienced professionals. Companies like DrainBoss, who operate across Sussex, Surrey, Hampshire, Kent, Brighton, and South London, offer reliable, family-run drainage services with no call-out charges — including emergency unblocking, CCTV surveys, and full drain repair.