Three-drop water radical on the left fixes the action: filtering is something done to liquids. Same radical drives the whole water-handling family - 洗 wash, 流 flow, 浇 pour, 滤 strain.
Right side supplies the sound: lǜ → lǜ (exact match). 虑's sense of 'sifting through thoughts' transfers nicely as a memory hook - filtering water is to liquid what considering carefully is to ideas, separating the wanted from the unwanted.
