Methods and washing tools are for combined cleaning of an annulus in a well across a longitudinal section of the well, and subsequent plugging of the longitudinal section. The method comprises: (A) conducting a perforation tool into a casing to the longitudinal section; (B) forming holes in the casing along the longitudinal section; (C) a washing tool conducted into the casing on a tubular work string, pumping a washing fluid through the tubular work string and out into the casing via the washing tool; (D) a directional device associated with the washing tool, conducting the washing fluid out into the annulus via a hole at a first location within the longitudinal section, after which the washing fluid will flow via the annulus and onward into the casing via a hole formed in at least one second location within the longitudinal section; (E) pumping a fluidized plugging material out into the casing at the longitudinal section; and (F) placing the plugging material in the casing and in the annulus along the longitudinal section so as to plug the casing and the annulus.