LONDON - British engineers say they have launched a "sewer war" against a giant fat blob clogging London's sewers.

Tuesday it is likely to take three weeks to dissolve the outsize fatberg.

They caution against expecting quick results as the fatberg is 250 yards long and weighs as much as 11 double-decker busses.

The unsavoury blob consists of congealed wet wipes, diapers, fat and oil.

Thames Water's Matt Rimmer says the fatberg is "a total monster and taking a lot of manpower and machinery to remove as it's set hard."

He said the task is "basically like trying to break up concrete."