Why you shouldn't pour cooking oil down the sink - and what to do instead

Rob Waugh

8 October 2025 at 11:39 am

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British households pour millions of litres of cooking oil down the sink each year, with around half of us admitting to having done so.

But doing so causes immediate problems, with coagulated cooking oils linked not only to blockages in the home (and expensive visits from a plumber) but also to huge 'fatbergs' in the sewer system, which form largely from oil and wet wipes.

But many of us are unsure about what to do with waste cooking oil instead, said Suzanne McKenzie, sales director at Lifecycle Oils, which recycles oil from Britain's food industry.

McKenzie explained: "Oil blocks up the drains and sewers, causing all sorts of problems for water companies and the environment. Most of the rest of the waste oil goes in the bin and ends up in landfill."

Why is cooking oil such a problem?

Beyond the fatbergs and potential blockages in the home, it's also extremely bad for waterways, explained McKenzie.

She told Yahoo News: "When oil gets into waterways, it's bad news for the wildlife that lives there. It reduces the oxygen levels in the water - suffocating wildlife, making the water toxic and disrupting the ecosystem."

Are some oils 'better' than others to put down the sink?

Some oils (like olive oil) stay liquid at lower temperatures, leading householders to wrongly assume that they are 'safer' to pour down the sink, McKenzie explained.

However, she told Yahoo News: "No oil should ever go down the drain."

Even olive oil will solidify rapidly in colder temperatures, McKenzie explained, meaning it's just as bad as more visibly 'solid' fats, such as animal fat from a roast dinner.

Olive oil starts to go cloudy at around 10C and solidifies at around 3C.

McKenzie said: "Even oils which remain liquid at low temperatures coat the pipes and eventually solidify, trap debris and cause clogs, and they still end up polluting our waterways."

What should householders do with waste oil?

When households end up with oily waste (for example, from a roast chicken), it's common to put the solidified fat into black bin bags.

But that just means that it ends up in landfill - whereas the high-energy waste is actually a valuable resource.

In areas with food waste collections, you can include cooking oil in your waste bin, which will be recycled into biogas and fertiliser (or composted, in areas with mixed garden and food waste collections).

But most household waste sites also collect cooking oil for direct recycling into biofuel.

McKenzie said: "Instead of throwing this oil away, people can collect it. Simply pour it into a jar or plastic container with a lid (let it cool first!), then take it with you on your next trip to the tip."

Freezing or chilling oil can help make it more manageable, cooling it into a solid block.

What happens to cooking oil after it's recycled?

When cooking oil is recycled, it's turned into biofuel, with plants in the UK able to produce millions of litres per week.

This is then used to fuel everything from vehicles to the refinery plants themselves.

McKenzie said: "The 18 million litres of used cooking oil we pour down the drain each year could become more than 15 million litres of biodiesel. That would be enough to power a car for more than 105 million miles, or 4,216 trips around the world. It would save 45 million kg of [carbon dioxide] CO2 as well.

"Unlike biofuels made from crops like palm oil or rapeseed, biofuels made from waste cooking oil don't compete for land used to grow our food. This means they don't drive agricultural expansion, deforestation or biodiversity loss.

"Biofuels made from waste provide huge carbon savings compared to conventional fossil fuels. Biodiesel from used cooking oil produces around 80-90% less carbon than fossil fuel diesel, and 40% less carbon than biofuels made from virgin feedstock."

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