Endless tasks

Here in the UK, if a task goes on and on we say "It's like painting the Forth Bridge".Today they finish painting the Forth Bridge. Thanks to new methods, it took (only) 10 years to do and the paint will last 20 years. So the 400 painters will have to find something else to do.

But what do we use now to describe an endless task.Is it pushing a boulder up-hill? Is it sweeping up the Autumn (Fall) leaves? Any suggestions?