Fats Oils Grease Blocking Drains | The Fatberg Warning

A 500-metre fatberg. Cleared by Thames Water engineers working from 16 February to 10 March 2026 beneath Poyle Road, near Heathrow Terminal 5. That's roughly the length of five football pitches, formed almost entirely from congealed cooking fat, wet wipes and food debris. Thames Water confirmed the clearance on 19 and 20 March, and the story did the rounds briefly before disappearing from the news cycle.

It shouldn't disappear. Because what happened under Poyle Road is the extreme end of something that happens on a smaller scale, every single day, in drains beneath residential streets and commercial kitchens across Greater London, including right here in KT3.

What Thames Water's Own Numbers Actually Say

FOG, fats, oils and grease, is not a minor nuisance on London's sewer network. Thames Water's figures are blunt:

That £40 million isn't absorbed quietly by a utility company. It feeds into bills. It delays other infrastructure work. And when a blocked sewer floods, the contents don't stay neatly underground.

The Heathrow fatberg is dramatic because of its scale, but the mechanism that created it is identical to what happens when someone in Malden Manor tips a pan of bacon fat down the kitchen sink.

What Actually Happens When Fat Goes Down the Drain

This is the bit most people get wrong. Hot fat drains away easily, so it feels like a problem solved. It isn't.

As fat cools in the pipe, it solidifies. Not immediately at the plug hole, but a few metres down where the water has had time to cool and the pipe narrows or bends. That solidified layer doesn't flush away with the next pour of hot water. It accumulates. Each cooking session adds another thin coat. Wipes, food debris and paper bind into it. Over weeks and months, the bore of the pipe reduces. Eventually, it blocks.

In a house on Green Lane or a terrace in Norbiton, that blockage might back up within your private lateral drain. You call someone out. Unpleasant, expensive, fixable.

In a shared sewer under a row of commercial kitchens in West Barnes or near Shannon Corner, the same process creates something on a different scale entirely. Multiple contributors, one shared pipe, no single owner watching it.

Why This Is a Shared-Sewer Responsibility Problem

This matters practically, not just philosophically. Under current legislation, Thames Water is responsible for public sewers, and individual property owners are responsible for their own private drainage up to the point where it connects. But when a blockage sits in a shared lateral or a public sewer, and it's been caused by FOG from multiple properties, establishing responsibility is messy.

What's clearer is liability. If your commercial premises discharges grease without adequate interception, and that grease contributes to a downstream blockage or flood, Thames Water can pursue the source. For restaurants and takeaways in Raynes Park, Tolworth or around Worcester Park, this isn't theoretical. Enforcement has happened.

For homeowners, the risk is more immediate and personal: a FOG-related blockage in your private drain is your cost to clear, full stop.

The Restaurant and Takeaway Issue in Southwest London

New Malden has a particularly dense concentration of restaurants, particularly Korean and Japanese, which involve high-volume cooking with oils, fats and broths. That's not a criticism, it's a fact of the area's food culture and economy. But it does mean the FOG load on local drainage is higher than in a comparable residential-only area.

A commercial kitchen producing 100 covers a night and washing up without grease interception will discharge a significant volume of FOG into the drains below. Multiply that across several premises on a parade, and the maths isn't pretty.

Grease traps and grease recovery units (GRUs) are the industry-standard answer. A correctly sized and regularly emptied grease trap intercepts FOG before it enters the drainage system. The key word is correctly sized. An undersized trap overwhelms quickly. An infrequently emptied one doesn't intercept anything once it's full.

If you run a food business in KT3 and you're not certain your grease management is adequate, it's worth having the drains below the kitchen CCTV surveyed. You'll see exactly what's coating the pipe walls. That evidence is far more persuasive than a vague worry.

What Homeowners Can Actually Do

The cool-and-bin method is not exciting, but it works.

• Let cooking fat cool in the pan.
• Pour it into a container (an old tin, a sealed bag, a jar).
• Put it in the bin, not the sink.

For washing up after fatty cooking, wiping the pan with kitchen roll before washing removes the bulk of the grease before any water is involved. A sink strainer catches food debris. Neither of these costs anything.

What won't work: pouring boiling water and washing-up liquid down the drain. This emulsifies the fat temporarily. It re-solidifies further down the pipe, often in a worse location.

Enzyme-based drain treatments can help slow accumulation in lightly affected pipes, but they're maintenance support, not a cure for an established partial blockage.

If You Already Have a Slow Drain

A drain that's slow but not yet blocked is telling you something. Don't wait for the full blockage.

A CCTV drain survey will show the condition of the pipe wall, where grease is accumulating, whether there's already a partial restriction, and whether the problem is purely FOG or whether a cracked joint or root ingress is making things worse. Root ingress and FOG accumulate together frequently. The roots catch debris; the debris accelerates blockage. Without camera footage, you're guessing at the cause.

High-pressure water jetting will clear an established grease restriction. For commercial drains, descaling jetting with a chain flail head removes the hardened material from pipe walls rather than simply pushing a channel through the middle of it. The difference matters for how quickly it re-blocks.

The Heathrow Fatberg Isn't an Anomaly

It's an accumulation. Twenty-three days of engineers working underground to clear something that took years to build. That's the end state of thousands of individual decisions to take the easy option at the sink.

I'm not trying to shame anyone. But when Thames Water is spending £40 million a year and Greater London still has 20,000 FOG blockages annually, the message from awareness campaigns clearly isn't landing widely enough.

If you're a homeowner in Motspur Park or Coombe and you've never thought about what goes down your kitchen drain, now's a reasonable moment to start. If you run a food business anywhere in KT3, and you're not confident about your grease interception arrangements, get them checked before you receive correspondence from the water company rather than after.

Drainsco covers New Malden and the KT postcodes, with engineers available 24/7. CCTV surveys, high-pressure jetting and grease management work for both residential and commercial drains. No call-out fee, and you'll have a clear price before any work starts. If you want to know what's actually happening in your pipes, the camera doesn't lie.