the ball is there for the following reason
the filter pot under the outer drum contains the plastic ball, when the drain pump starts the action of the pump draws the ball downwards allowing water out of the drum. when the pump stops the ball floats up to the top of the water in the pot and seals the hole
this was devised to try prevent the dirty water from the sink filling the washer if connected this way., another method tried was the flap valve mounted on the pump output
wirecutterman
May 2010