Its a "Venturi" type of suction system. There should be 2 hoses in the bottom of the bilge that go back to the pump. When water runs through the pump it creates suction in the hoses that remove water from the bilge. It only works when the ski is running, and is useless when the engine is off, or if it becomes clogged.
There have been many many complaints about this system. It can get clogged and stop working, and end up sinking your ski. There are many guys that highly recommend adding an electric bilge pump to the ski. Look at this recent post by Outlaw, who described how an electric pump saved his ski: http://www.pwcforum.com/general-pwc-...ilge-pump.html
. Do a search on "RXT bilge pump" and I think you will find plenty of information.