Assuming you have an Apex or Apex Lite, all you would need is a breakout box and a couple float switches. If you have an Apex Jr, then you will also need an expansion module PM(1,2, or 3) in order to gain the ability to read switches.
Then it is just a matter of programming the desired behavior. If you have not read it yet, the New Users Guide is stickier at the top of the forum or can be found on the Neptune website. It has loads of info on setting things up.
Todd