They 'flushed' impurities from the system. = They 'flushed' impurities out of the system.
She published her first novel while still 'in the flush of' youth. [=while still young]
The committee succeeded in 'flushing out' [='finding'] several good candidates.
(..) I see you. I see it. I see it. You know, we can get this thing, Mac. You work your way down there toward him. I'll get in back of him, flush him toward you. When I flush that son of a bitch, you nail him. I got a score to settle. We've both got scores to settle. Come on. Quickly. Hurry up. (..)1987 Predator