氵 is the left-side form of 水 (water). It supplies the leak-and-discharge image — water finding a way out — and extends naturally to figurative leakage of secrets (泄密) and venting of emotion (发泄).
世 shì provides the sound, shifted to xiè. The same phonetic feeds 蝶 (dié, butterfly) and 牒 (dié, official document) when the underlying 枼 stem appears — a cluster around the dié/xiè/shì sound space.
