A sinkhole filled with fat and rats has prompted a North Island council to educate its residents on how to get rid of grease.
The small sinkhole appeared on Station Street in Dannevirke last month, when the road gave way to movement below the tarmac.
The council's roading contractors found a large build-up of fat inside the hole and rats feasting on the waste, Tararua District Mayor Tracey Collis said.
She was shocked to see so much white grease plastered around the sewer.
"The fat looks like a wave breaking in the pipe," Ms Collis said.
Fast food company KFC and other smaller fast food outlets operate nearby, but Ms Collis said they were unlikely to be responsible.
"Those businesses have food safety and waste management plans and follow best practice with grease traps," she said.
In a statement, the KFC restaurant said all its used oil was discarded into drums onsite and other grease is disposed of through greasetraps.
However, a Watercare spokesperson Peter Rogers says greasetraps at fast food outlets can become inadequate.
"It may change hands and you've got double the volume going through or the capacity,
"And there's also the education of the staff as well in terms of a lot of food restaurants will dispose of waste oils to a recycler but then you've got your washing of your plate and ensuring that those are segregated out into the solid waste."
It had more than likely come from households, she said, which prompted the council to update best practice guidelines online and discuss the issue in the media.
Washing greasy dishes in sinks and using insinkerators could be part of the problem, she said.
While there was not a rat infestation, Ms Collis said, there may be more rats hiding out of sight.
The sinkhole has been repaired, the drain has been water blasted, and the council will run cameras through other parts of the system to check for more build-ups.