Augean stables (the)

the Augean stables - авгиевы конюшни
clean the Augean stables - чистить авгиевы конюшни, совершать неблагодарный труд

Usage: The expression is sometimes used in literature to describe a very difficult unpleasant job.
According to ancient Greek stories, the very dirty buildings where a king named Augeas kept thousands of cattle. Hercules was ordered to clean them, and he did this by changing the direction of a river to make the water flow through the stables.