Up to 20 tonnes of sewage from cruise ship passengers will be held on the liners at the Auckland waterfront by the end of the Rugby World Cup.
During the weekend of the finals, four cruise ships will be berthed at the wharves, and their 8000 passengers and staff will eat, drink - and retire to their cabins at night.
McKay Shipping managing director Craig Harris said the ships would hold all their sewage on board as they parked in the same place for longer than usual, up to four days.
International guidelines directed that the sewage be dumped 20 miles from the coast once the ships re-embarked on their voyages, Mr Harris said.
The waste would be chemically treated before being dumped, and some of the ships had facilities to convert sewage into drinking-quality water.
Meanwhile, grey water - from laundry and washing - would be taken away on barges, and fresh water piped from the wharves.
Engine-room sludge, if built up, is to be sucked out of the liners and transported to recycling centres.
The cruise ships will used four wharves during the finals weekend. The Rhapsody of the Seas will be at Princes Wharf, the Pacific Dawn at Queens Wharf, the Volendam at Captain Cook Wharf and the Orion at Bledisloe Wharf.
Mr Harris said the final mix of passengers was not yet known, but most would be Australian. Big groups of South Africans were also booked.
The Pacific Dawn was expected to be a British stronghold - as it had been for the Lions' tour eight years ago.
There will be eight other cruise-ship visits during the tournament.
The average person is estimated to make just over 1kg of sewage waste a day.
OUTPUT
Sewage production during the World Cup finals:
Volendam
1432 passengers, 615 crew, 4 days, 8188kg.
Orion100 passengers, 75 crew, 3 days, 525kg.
Pacific Dawn
2020 passengers, *660 crew, 3 days, 8040kg.
Rhapsody of the Seas
2435 passengers, *765 crew, 1 day, 3200kg.
*unofficial sources