Abstract: A method of cleaning a liquid which is conducted centrally and from the top in a strainer provided with a closed casing within a centrifugal drum. The bottom of said strainer is formed by a screen and is shut off at the top by a cover comprising screen holes and a central opening. During the centrifuging of the liquid a fluid jet is directed to the rotating cover in situ of the screen holes, while the water emerging from the screen holes is collected in a housing surrounding the drum and discharged.