Pouring oil down the sink creates 'fatbergs'. Here's what to do instead

Jan 14, 2024

By Patrick Wright

You might have heard about "fatbergs" — congealed masses of fat, wet wipes and other detritus that cause all sorts of problems for sewer systems.

Back in 2017, a 250-metre long fatberg described as being "as heavy as 11 double-decker buses" clogged up a Victorian-era sewer in London for weeks.

Fatbergs cause problems in Australia, too, particularly in winter. That's because cold temperatures help fats and oils solidify.

"Fatbergs are a significant problem," says Iain Fairbairn, head of wastewater and environment at Sydney Water.

"Many people are not aware of the enormous environmental damage and cost associated with flushing the wrong things down the toilet, or pouring oil down the kitchen sink."

Ian Wright, associate professor in environmental science at Western Sydney University, says leftover fats from roast meats can be particularly problematic.

He explained to ABC Sydney Breakfast that, once cooled, these fats can act as a "glue" that can turn sewer waste into an "unmentionable blockage".

"Say you've had a roast, a lot of the fats will be liquid. It is so tempting to … mix [that oil] with water and wash it down the sink into the sewer," he says.

"Particularly when it's so cold, that [oil] will harden when it cools down. That can form a blockage of the sewer.

"It could be in your property, it could be down the road, it could be a giant sewer main — and it becomes everyone's problem."

When it comes to disposing of fats and oils, it's best to check the rules with your local council or waste authority.

But, as a general rule, Dr Wright says cooking fats and oils can be disposed of in landfill once they've cooled down.

Fatballs and their bigger, uglier cousin — fatbergs — occur when various oils and fats combine with other chemicals and materials that get tipped down the drain.

"Many people use an old waste container to dispose of animal fat, like a yoghurt container," he says.

"[They] pour it in when it is still hot, wait for it to cool down and then throw into the rubbish for landfill."

You can use your fridge and your freezer to help the oils and fats solidify.

"For small amounts, absorbent paper towel can soak up lots of fat, oil and grease — and then throw into the bin," Dr Wright says.

Many councils offer options for disposing or recycling fats and oils, which can be particularly useful if you're dealing with large quantities.

"Every fish and chip shop now recycles all their used oil. That can actually be converted into fuel for diesel vehicles," Dr Wright says.

Planet Ark's Recycling Near You website can help you find recycling options in your area.

Sydney Water has some simple advice when it comes to the kitchen: only water and soap should be going down the sink.

That means no coffee grounds, oils, grease or food scraps.

Even "insinkerators" — which process food waste into small particles before flushing them down the sink — can cause problems.

Some councils are calling on residents to ditch these devices and compost their food scraps instead.

We also need to be careful with what is flushed down the toilet.

Wet wipes create up to 75 per cent of all blockages, according to Sydney Water.

Dr Wright says other common bathroom items can also cause problems.

"Hair, wet wipes, cotton tips and other things … should not be flushed into the sewers. But lots of them are," he says.

In the past, the ACCC raised concerns about wet wipes that were marketed as "flushable".

However, new standards introduced last year make it harder for companies to claim their products are safe to flush.

"Wet wipes/flushable wipes are a massive problem, and they twist like rope," Dr Wright says.

"They also are often triggered by tree roots acting as a gathering point that starts the build-up — until the sewer becomes totally blocked."

So what is safe to flush down the toilet?

There are only three things: pee, poo and paper.

Everything else is better off in the bin.

This article is based on an interview with Dr Ian Wright on ABC Sydney Breakfast on June 26, 2023.

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