Genital Washer is the former slave of the unnamed Slaveowner from the Post-Apocalyptic Dimension, and the younger brother of Taint Washer. His sole purpose is to wash the genitals of his master, and he was named specifically after his purpose. He appeared in "Rickmancing the Stone".
At some point in his life, he was captured together with his parents and brother, and were sold as slaves to an unnamed man, later, his parents died.
Genital Washer is a slave in the Post-Apocalyptic Dimension employed by Slaveowner to specifically wash his genitals, alongside his brother Taint Washer. One evening he is washing Slaveowner, who threatens to ship Taint Washer to the wastelands if he touches Slaveowners genitals again. Before the Slaveowner finishes his threat to Genital Washer, Morty Smith and Armothy jump in through a window. Genital Washer and his brother run out of the room.
The fate of Genital Washer is unknown, but it is likely that he and his brother have been released after the death of their master, and have resumed a new life.