Visitors to Abel Tasman National Park this summer are being reminded to be responsible with their rubbish, in a bid to avoid a messy problem.
Each year more than 200,000 people walk through the park, staying at campsites and using the toilet facilities.
Department of Conservation senior ranger Tom Young said each winter about 150,000 litres of sewage was pumped out, by truck or barge.
"At the end of autumn we go around all the toilets and estimate how much waste is in those tanks and then we contract the operation out to one of the local contractors," he said.
The man hole covers at the toilets are opened and the barge pumps the waste out of the tanks and onto the tanks on the ship.
"In general things go reasonably well, but we do have a bit of an issue where visitors, who probably don't think it through, put things down the toilet. Things like wine bottles and carrier bags full of rubbish.
"They put all their rubbish in a carrier bag and they've thought 'oh, what am I going to do with this?' And they've shoved it down the toilet, very much out of sight, out of mind," Mr Young said.
That becomes a problem for contractors removing the waste, because their equipment is not designed to suck up bottles or bags and there is potential for the equipment to get blocked.
"We have to fish the bottles and carrier bags out of the toilet tanks during the operation," which he described as an unpleasant and time-consuming job.
"It's a shitty job, but someone's got to do it."
Something similar to a hay fork was used to pick the items out of the tanks, which can be up to two metres deep.
While most people followed the rules and took their rubbish out of the park, the department did not provide rubbish bags or waste facilities.