get to the bottom of somethingUsed to mean investigating or clarifying a confusing or uncertain situation. In natural French, “quelque chose” is usually replaced by a specific noun or pronoun, as in “tirer cette affaire au clair” or “tirer ça au clair.”
FR: Nous devons tirer quelque chose au clair avant de prendre une décision.
EN: We need to get to the bottom of something before making a decision.