"Normally they’re not that big, but I have heard of one in the UK that was the size of a double-decker bus." Mr McCafferty said the monstrous piles of rags, paper towel, sanitary products, wet wipes and fats were becoming an increasing problem in Melbourne. The Wallan fatberg was taken to landfill once removed. Loading Replay Replay video Play video Play video "Society is shifting to other products and putting things down toilets that they shouldn’t, so when you already have fats and oils down drains – they shouldn’t be there either – that combines with these materials that aren’t biodegradable to the extent that toilet paper is, and eventually you get this congealed solid mess," he said. "They block sewers and cause costs to extract them, but ultimately if we don’t get to them quickly they can result in sewage spilling into the environment or people’s properties."

Mr McCafferty said his staff estimated the 42-tonne Wallan fatberg took only three or four months to build up, but he said it was not related to more people being home because of coronavirus. However, Yarra Valley Water has been noticing some other recent changes that are related. "Nothing concerning, just interesting," Mr McCafferty said. "We are seeing the morning peak is a little bit later, in water use. And we see another peak at lunchtime that we don’t normally get, this is in residential areas. So you can tell obviously more people are at home. "There’s a significant reduction in sewer flows in the CBD. The profile is changing and commercial businesses are seeing a little bit of a reduction, like shopping malls and those sorts of things."

Loading Meanwhile, some plumbers have experienced a boom in emergency callouts as people clog their drains with toilet paper substitutes during the coronavirus lockdown. In late February and early March, toilet paper shelves in supermarkets were stripped bare by shoppers, and some households turned to using baby wipes, paper towels and even bed sheets as a stand-in. Don Arscott, who has run Melbourne 24 Hour Plumbing for two decades, said that in the weeks when toilet paper was scarcely available he unblocked twice as many drains as usual. "I had one family cutting up bed sheets to wipe their bums," Mr Arscott said.