Mr Paul Andersen (from Bozeman High) describes Osmoregulation (including in fish which you don’t need to know) in a 8m 57s lesson.
Osmoregulator or Osmoconformer? Here are two videos about contractile vacuoles in Paramecium (they are osmoregulators): Paramecium vacuole (1m video) and contractile vacuole (a 27s explanation). If it goes wrong – Paramecium exploding!
A nice introduction to how the kidneys work (from TED-Ed):
A superb flash animation on the Kidneys from kscience.
In Crash Course Biology #29 – The Excretory System: From Your Heart to the Toilet, Hank takes us on the fascinating journey through our excretory system to learn how our kidneys make pee.