Coule
C’est un homme à la coule (pop.) = He is a smart, knowing chap.
[Compare: Il la connaît dans les coins, celui-là = He knows his business in every corner.]
Couler
Ce qu’il dit coule de source = What he says comes from the heart, comes fluently from his lips.
Cela coule de source = That follows naturally.
Couler à fond = (of ships) To founder; (of persons) To be ruined.
*Il faut laisser couler l’eau = What can’t be cured must be endured.
Coulisse