to pour
汋 centers on the act of pouring liquid, specifically water. The single given meaning is straightforward and concrete.
汋 combines 氵 (water) with 勺, which likely contributes the sound and may relate to a ladle or pouring action. The exact historical development is uncertain.
Water 氵 is poured from a ladle-like shape 勺. Imagine a stream of water flowing from the curved 勺 into a container.
For サク, picture pouring water into a sack: sack -> サク, and the water flows from the ladle into the sack.