Underpants flushed down the Interislander ferry's loo have been revealed as the cause of an eruption of human urine that showered down on a passenger's car.
The spray happened as maintenance staff worked to clear a toilet blockage on Monday's 9am ferry journey from Wellington to Picton.
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Sean Scanlon - his wife Lucy, their son Jack, 8, and their dog - were among the 1000 passengers on board and sitting in their car in the direct firing line.
Scanlon told the Westport News newspaper his family had wound down their windows due to the stuffy weather when they noticed two Interislander workers busy with drums and pipes. Then something went wrong.
"There was a shower of liquid and an immediate odour," he said.
Some of the urine raining down on the driver's side of the car hit Scanlon and his son.
"It was a 'wee' mistake," he joked.
"They were fiddling around with these blue drums, then we got a golden shower."
The workers were also drenched in the urine.
One was standing nearby "in white overalls looking absolutely horrified, totally drenched in pee".
Interislander executive general manager Walter Rushbrook has apologised to Scanlon's family and offered them compensation.
He said the blockage "turned out to be caused by a pair of underpants flushed down an onboard toilet".
"The ferry's toilets are a vacuum pressure system, and we have signage to advise that only the toilet paper supplied can be flushed down," he said.
As part of the workers' efforts to locate the blockage, an "unusually high pressure" built up that ultimately led to the "leak", Rushbrook said.
He said Interislander ferries - owned by KiwiRail - were often running at peak capacity this time of year as more than 1000 people sailed on popular daytime voyages.
"We only have a relatively short amount of time between sailings to load and unload the ships plus attend to urgent maintenance issues, which is why we were trying to trace the blockage issue at the time the ship was discharging vehicles," Rushbrook said.
The workers clearing the blockage were wearing standard protective gear at the time of the eruption and had taken preventative immunisation shots.
"As with all incidents that occur we will review our processes and procedures," Rushbrook said.
Scanlon said he complained about the incident on Monday but didn't get a call back until Friday.
"We have contacted the family and apologised that our call centre did not escalate the matter appropriately so that their calls could be returned in a timely manner," Rushbrook said.
"We are investigating why the calls were not escalated."
Scanlon also expressed concern for the workers.
"As a worker, it would be a pretty miserable thing to happen.
"It's also not a very good look to be spraying passenger cars with human pee."