leak
泄 centers on liquid or gas escaping from a container: leaking out, seeping, or dripping.
泄 combines 氵 (water) with 世, which likely contributes the sound and the idea of spreading or passing through, suggesting water leaking or seeping.
Water 氵 passing through the world 世: imagine a world where water always finds a crack to leak through.
For セツ, picture a set of pipes leaking water: set -> セツ, and the water drips out.