You use toilet, then flush. Instead of the toilet filling the tank as usual, it pumps it out of the faucet where you can wash your hands in the 10-20 seconds it takes to fill the tank again. The water that you used to wash your hands then falls into the tank as usual. When you flush again, it flushes the “grey” water…

I usually wake up to some blessthefall or Disturbed, occasionally August Burns Red.