Police closed Durrington Lane between Greenland Road and Pond Lane earlier this morning due to the overflow.
A Southern Water spokesman said: "Our contractors and an Investigation Technician were called to the site and confirmed two manholes had overflowed.
" Specialist equipment was used to clear a fat blockage at around midday today, which stopped the spill.
"The road was then cleaned and disinfected.
"The Environment Agency were also present on site and our Network Protection Officer and Fats Oils and Greases team will continue to investigate.
"This incident underlines the importance of our Unflushables campaign - the only things that should go down your loo are the three Ps - pee, poo and paper.
"It's also important not to dispose of fat, oil or grease down your sink or drain - and this is especially important for food businesses.”
The road was reopened this afternoon after cleaning work was completed.