Disclosed are a washing unit for washing contaminants within a washing machine, a permanent magnet inducing unit for effectively washing an inner wall of a water tank by using induction of an electric field or providing a motion to an artificial floating body of the water tank, and a drain cover for a washing machine for assisting a washing operation of a washing ball of the washing machine. The washing unit has a body for maintaining a certain shape such as a ball and a plurality of washing projections, and is introduced into spaces between the water container and the washing tub and between the water tank and the pulsator to frictionally remove various filths attached to the washing tank, the washing tub and the pulsator with the washing projections that floats at a predetermined depth of washing water.