Hamlet wants to wash his memory clean, as one would wash dirt down the sink. The things his mother has done to him and memories he no longer wants would be dumped in the sink and washed away by the facet. By marrying his uncle, and her brother, she has, to him, pulled the last straw. He no longer has total respect for his mother because of that. Also knowing that Claudius has killed his father and is now sleeping with his very own mother, and is blood related, is one ultimate betrayal to Hamlet. He feels as though he is now neglected and unimportant now that his father is dead. He says it's an "unweeded garden" that eventually spreads to the theme of decay throughout the play as almost everyone dies. Hamlet would want nothing more than to wash his feelings of betrayal and neglect down the drain and just wash them all away. He watched Ophelia fall and eventually drown. Those are all feelings he no longer wants to have to "move on" because he was in love with Ophelia. She betrayed him also, because of her controlling father. By deceiving him and helping Polonius spy on him was too much for Hamlet to take in. Hamlet seems to go mad throughout the play until finally he's exiled and comes back as a different man, as if his "problems" were washed away and he is seeing things in a different light. He stops wearing black and actually seems to be thinking logically and not so nutty. He knows that he wants to avenge his father's murder by Claudius but seemed to have gotten the "images" out of his head so that they are insignificant in the face of their betrayal. He erased those images in his memory so as to not be deceived again. With his memories erased, Hamlet was able to properly avenge his father's murder. .
