through the mill

through the mill  {adv. phr.}

1. Experienced.

You could tell immediately that the new employee had been through the mill.

2. Through real experience of the difficulties of a certain way of life.

Poor Jerry has had three operations in one year, and now he's back in the hospital. He's realty gone through the mill.

Compare:

GO THROUGH HELL AND HIGH WATER,

COME HELL OR HIGH WATER.