donkey

donkey work the boring or laborious part of a job; drudgery.

2005The Register I get the Systems guys to do all the donkey work once I'm sure it's up and running properly.

for donkey's years for a very long time. informal

☞ For donkey's years is a pun referring to the length of a donkey's ears and playing on a former pronunciation of years as ears.

2013Daily Telegraph Mrs Lynch said the stealing had gone on 'for donkey's years', and the family had to go to court as a last resort because 'we just couldn't go on'.

talk the hind leg off a donkey: seetalk.