Abstract: The invention relates to a method for cleaning an outer surface (1) arranged at the bottom of a tank (3), a vessel or similar, said method comprising the steps of: generating and supplying a pressurized cleaning fluid by means of a production source (2) of pressurized cleaning fluid, the fluid pressure being between 3 and 12 bar; conveying the cleaning fluid opposite the said outer surface (1) of the tank (3) by circulating the fluid in a pipe network (4) arranged below the tank (3); cleaning the outer surface (1) of the tank (3) by means of a plurality of rotating jets of cleaning fluid, the said plurality of jets being generated by at least one multi-jet rotating head (10) connected to the pipe network (4), wherein conveying of the cleaning fluid is realized by the pipe network (4) forming a closed loop (5) arranged below and near the centre (6) of the outer surface (1) of the tank (3), the said closed loop (5) being supplied with cleaning fluid by a feed pipe (7) connected to the said production source (2)