slave away at something
To work strenuously and continuously (doing something). I slave away over a hot stove all afternoon, and you can't even be bothered to finish what's on your plate? I've been slaving away at this report for the last three days. I'm just ready for it to be finished! I refuse to slave away for minimum wage
slave away (at something)
in. to work very hard (doing something). I’m slaving away for $7 an hour and have no prospects for the future.