Washing one's hands is an idiom in China.
Original intention: the ceremony held after the boat people who transported food to Chang 'an Palace landed at Weihe Ferry in Han Dynasty to show the achievement of official position;
The latter refers to: some underworld figures are ready to enjoy their old age after they get rich and publicly declare their repentance;
Now also refers to: give up the industry or thing you have been engaged in for a long time.