Blue chemicals had been spread over the sewage - which luckily the man said was masking the smell.
"It's stinky, but it's mostly the chemical smell and luckily it's quite windy, too," he said.
He said there were lots of cyclists and joggers passing by "looking a bit put off."
The fire service was called to the scene, at Patiki Rd, at 10.30am.
The spillage is adjacent to Prestige Loos - a port-a-loo business which carries the slogan "No 1 in the No 2's Business."
The company could not be reached for comment.
A fire service spokeswoman said the spill has been contained, and staff from a nearby business have been tasked with the cleanup.
Auckland Council has been notified of the spill, the spokeswoman said.
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