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 get headaches, it's so bad. It's like, they just never go away, you know. The President should just clean up this whole mess here. He should flush it right down the f$cking toilet. I think I know what you mean, Travis. But it's not gonna be easy. - We'll have to make some radical changes. (..)1976 Taxi Driver