Sisyphean Task
Refers to a task that is both laborious (perhaps endless) and ultimately futile.
EverydayConcepts.io
Reference entry — no illustration yet
Origin
Named for the Greek story of Sisyphus who was punished for his self-aggrandizing craftiness and deceitfulness by being forced to roll an immense boulder up a hill only for it to roll down when it nears the top, repeating this action for eternity.