The University of Otago archaeology masters student was on site in May when one of the city's first waste pipes was uncovered under the former NZ Road Services building.
Excavators were digging a lift shaft for the Otago Settlers Museum redevelopment and came across the hand-made, 30cm diameter earthenware pipe.
"I was just so excited," Mr Williams said.
The pipe, and another found in March last year, were 1.7m below the surface and were significant because they were so old.
In 1862, work was begun to remove Bell Hill and reclaim land in Otago Harbour.
Mr Williams believed the pipes would have been laid in sections as the land developed.
Before the drainage system was laid, waste built up in the city streets, creating health concerns and disturbing residents.
Mr Williams believed drainage pipes were not given the archaeological attention they deserved and he wanted to change people's opinions towards them.
For the past year, he had been studying early Dunedin's drainage system, and the characteristics of old pipes, for his master's thesis.
Ultimately, he wanted to create a standardised approach to their analysis.
Museum director Linda Wigley said the find was "quite neat".
"We are really interested to find out more about it. It's great we have the expertise here."
She was unsure what would happen to the pipe and would wait for the Historic Places Trust to make a recommendation.
