To flush out this point, consider that hiring someone is not free. There can be significant costs of hiring someone who performs poorly (opportunity cost, training overhead, lost work).
Grammar is about sentence structure; your point is about word choice, otherwise known as "diction."
And "flush" is perfectly correct. Used transitively, it means "to expose or chase from a place of concealment." Example: "the hunters used dogs to flush their game from the bushes."
In figurative language, "flush" is a good choice when you're talking about stripping away extraneous information. "Flesh" is used when you're proposing to add more information, as in putting flesh onto bones.
I should add that I'm only addressing your claim that "flush" is inherently scatalogical, not whether the original use was valid.