swamp
澤 centers on a wet, low-lying area: a swamp or marsh. The given meanings focus on this single concrete sense.
澤 combines 氵 (water) with 睪, which likely contributes the sound and may relate to a marshy or watery place. The exact historical development of 睪 is uncertain.
The left side is water 氵, and the right side 睪 looks like a complex tangle of plants and earth. Picture a waterlogged area where reeds and mud intertwine: a swamp.
For タク, imagine a tack stuck in the mud of a swamp: tack -> タク, and the tack sinks into the wet ground.