"Bladder is like a district official; it stores the fluids so that they can be excreted by its action of Qi transformation."
Bladder has wider sphere of activity than in Western medicine. Stores/excretes urine but also has role in transformation of fluids necessary for the production of urine.
"Dirty" or "impure" part of fluids is sent by Small Intestine to the bladder, which further transforms them into urine. Bladder then stores and excretes urine.
Bladder function of transforming fluids depends on the Kidney Yang. If Kidney Yang is deficient, Bladder will lack Qi and heat to transform fluids and symptoms will include profuse, clear urine, frequent urination or even incontinence.
Bladder and Small Intestine both depend on Kidney Yang and both work together to move fluids in Lower Burner.