Behold the 'monster fatberg that's lurking under the street' in London

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There's a 130-tonne "monster fatberg" made of oil, grease, fat, diapers and baby wipes wreaking havoc in the sewers of London. 

"It's not a nice smell. The way I would describe it is probably a mixture of rotten eggs combined with a nasty smelling public toilet," Alex Saunders, the waste networks manager for Thames Water told As It Happens host Carol Off. 

Saunders' team is charged with trying to dislodge the 250-metre long blob clogging one of the city's Victorian sewers in Whitechapel.

The fatberg formed, he said, because of people flushing things down their sinks and toilets that absolutely do not belong there —  fat, oil, grease and sanitary items, to name a few. 

"What happens is the fat hardens and it mixes with these sanitary items to form a very hard, almost concrete-like blockage in the sewers and it gives us real, real problems in terms of keeping the sewers flowing every day," Saunders said.

Once the process starts and then more comes through, it grows and grows and grows.- Alex Saunders, Thames Water

"Our sewers are a bit like arteries in your body. So when it leaves your house, it goes down the smaller arteries you might find in your hands or in your feet and then it eventually gets to one of our bigger sewers like your main arteries near your heart. And just like if you have a bit of a fatty diet, your arteries clog up with fat. That's exactly what happens in the sewers."

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And they can't just flush it out, he said.

"The fat clings to the sides of the sewers, no matter how much is flowing through," he said.

"And the sewers are quite cold places, so the fat dries and hardens and then once that process starts and then more comes through, it grows and grows and grows. And that's how we've got the monster fatberg that's lurking under the street in Whitechapel in London that we're trying to tackle."

Workers, he said, are using equipment that blasts the fatberg with high-pressure jets of water, breaking it down into "manageable chunk-sized pieces."

"Then, in this instance, it's actually a case of our guys getting down into the sewer, getting dirty, getting very wet, and actually manually pulling this stuff back out of the sewer. And then once we get it back to our manhole, our chamber, we then suck it out into big tankers and take it away."

It's dangerous work, he said, and extremely difficult. 

"Imagine carrying a big rock with both hands. Now imagine doing that in a cramped sewer, bent over with sewage lapping at your feet," Saunders said.

As of Wednesday morning, Thames Water had managed to chip away at about 80 to 100 metres of hardened fatty sewage, but that's just the tip of the fatberg, so to speak.

There's another 90 tonnes of the stuff to get through. The process is expected to take weeks.

As the work continues, Saunders has a straightforward message for the people of London.

"The really easy way that we like to remind our customers about what should and shouldn't go down the toilet and down the sink is remember three Ps — them being pee, poo and toilet paper," he said. "Anything else is a definite no-no."