Abstract: A washer is described for cleaning the interiors of tanks that hold milk, beer, chemicals and so on. A body 2 reciprocates relative to a substantially surrounded and relatively fixed piston 19. The body 2 oscillatably supports three nozzles 7 each of which is movable through an arc of 60.degree. and which arc is angularly spaced from those corresponding to the other two nozzles 7 by further angles of 60.degree.. However, the body 2 and nozzles 7 are also indexed, during operation, in steps, around a further axis which is perpendicular to, and offset from the axis of oscillation and which substantially corresponds to the longitudinal axis of the tank washer itself. Thus, each nozzle 7 cleans not only an arc of 60.degree. but rotates that arc through 360.degree. so that the whole of the interior of a tank is both washed and substantially rinsed by the three nozzles 7.