Watercare has named five Auckland suburbs where too much oil and fat is being washed down drains.
Solidified fats cause pipes to block and sewage to overflow and the clean-up costs $6 million a year.
If you pour cooking oil down the kitchen sink, you could be feeding a fatberg.
"If this stuff goes down the drain - it might be hot when you put it down - it becomes cold and it hardens, it starts forming a thing like this which is pretty gross," said Watercare chief customer officer Amanda Singleton, holding up a demonstration fatberg.
But not every Kiwi cook knows it's a no-no.
"Chuck it down the sink," one told Newshub.
"People kinda think when it's hot it will slide down the drain and enter the sewer, which it does, but then it becomes cold and as it becomes cold it hardens," Singleton said.
The solidified fats cling onto items that also shouldn't be in the sewers, like wet wipes.
"It creates blockages and really it causes the sewage to go somewhere, which is out the drain," said Singleton.
So if it clogs the drain it can cause overflows.
Watercare took to social media naming Auckland's suburbs that are in the 'bad books' this month for pouring fats, oils and grease down the sink. They are Henderson, Mangere East, Mt Roskill, Avondale and Highland Park.
And it's no small problem - these blockages cost the council $6 million a year to clean.
"I'd like to spend that providing more resilience in our network," Singleton said.
The suburb of Henderson frequently has fatberg blockages, but some locals know the rules.
"I leave it to sit until it goes hard and then I put it in the rubbish. Don't put it down the sink though," one told Newshub.
"Council is busy rolling out the little food scraps bin. I'd put it in those bins," Singleton said.
If the thought of sewage running in the streets isn't enough to put you off, spare a thought for the workers who have to remove this revolting stuff.
