Yorkshire Water ordered the outfall pipe as part of a £26million scheme to build a new wastewater treatment facility further inland.
The relocation is necessary because the current site is threatened by coastal erosion - Withernsea's cliffs are among the fastest-eroding in Europe.
The new pipe was moved into place earlier this week and will now be sunk into the seabed.
It was transported across the North Sea from Norway.
Yorkshire Water project manager Matthew Brown said: “This scheme marks a substantial investment in Withernsea and the arrival of the new outfall pipe is a significant milestone in this important project.
“Work off the coast is due to continue until September as installation and checks are completed.
“During the dredging of the seabed in recent weeks we have not observed adverse water quality. However, we are continuing to monitor the bathing water throughout the duration of the works and the advice against bathing notice will remain in place as a precaution, in order to ensure public health is protected.”
The new treatment works, which are expected to be completed in summer 2021, will service wastewater for 15,000 people and be built using the more environmentally sustainable Aero-Fac system, with a low-carbon construction producing minimal odour and noise. It will have no need for sludge removal, meaning no tanker movement and a reduced impact on traffic as a result.
Norway and the Holderness coast are enjoying a close relationship at the moment as the battle to prevent cliff erosion destroying homes and businesses continues.
Earlier this month a large consignment of rocks from the Rekefjord quarry on the country's southern coast were shipped to Withernsea, where they will form part of a new sea wall to defend the town.
Five thousand tonnes of granite-like rock called anorthosite were imported by sea for the defences to protect the Golden Sands holiday park and Holmpton Road.
It took three days to sail the cargo across the North Sea and aother five days waiting off the coast until weather conditions were good enough to bring it ashore by barge.
The finished sea defences will be made from 63,000 tonnes of the rock and the project will be completed by the end of 2020.
The interlocking structure is designed to prevent wave action from reaching the cliffs, thus reducing coastal erosion. The largest rocks on the outside weigh up to 10 tonnes.
When complete, it will extend the current defences with 400 metres of rock armour, and will include a new 100-metre rock structure at the end of the defences.
A £3million grant, which allowed the £7million scheme to go ahead after other bids had failed, was provided by the European Regional Development Fund at the end of last year.
On this stretch of coast around four metres per year of land is being lost to the sea, but this has recently risen to six metres. Last year around 12 metres were lost off Golden Sands .