sieve, to sift, to strain
簛 centers on separating fine particles from coarse ones using a meshed tool: sieving, sifting, or straining.
簛 combines 竹 (bamboo) with 斯, which likely contributes the sound. Bamboo was traditionally used to make sieves, so the character suggests a bamboo sieve.
Bamboo 竹 over 斯: imagine a bamboo frame with a mesh made from split bamboo strips, used to sift flour or strain liquids.
For シ, picture a sieve made of bamboo that you use to sift tea leaves: the word 'tea' sounds like シ, and the bamboo sieve strains the tea.