Bladder

膀胱 pángguāng is the hollow, yang organ (府 fǔ) related to the water phase. It stores the body’s fluids, and when required they are transformed and excreted.

This also covers the excretion of fluids through sweating, giving the bladder a much larger role in fluid metabolism than is implied by the organ name. Its yin–yang property is considered greater yang (太陽 or 太阳 tàiyáng).