But contractors working on the Dunedin City Council Tahuna sewage outfall pipe did just that successfully yesterday.
Specialist staff from AAA Concrete Pumping were brought in from Marlborough and Queenstown to pump 190 cubic metres of concrete along the length of the construction pier and into an underwater steel structure.
The resulting concrete block will securely hold in place two outfall pipes - an underground pipe laid from the Tahuna sewage treatment works and a 1km long marine pipe - to enable a short joiner pipe to be placed between them.
It was important to "hold things together", council project manager Brian Turner said yesterday.
"The pipes will join approximately 9m below the surface and 5m below the seabed, so this is the most critical area to get right."
Pumping began at 7am and was finished by 2pm.
The job was the most challenging AAA Concrete Pumping had attempted, administration manager Paula O'Donnell said yesterday.
"The distance was the farthest we have ever done . . . What the guys did takes a lot of skill, but it all went very smoothly."
The $37 million pipe project has been delayed by rough weather, but Mr Turner said pressure testing was expected to take place next month, with the pipe expected to be commissioned in December.
