Sliding Float

Hi all, I was rthinking of going to a small lake at the weekend, the depth there is over 15 feet, I would, hopefully like to try a sliding float with a slip knot. Could anyone tell me, or show me, how to to set it up please ? I would also like to know how to plum the depth, since the float is sliding how do I know what depth i'm at ? Your answers will be eagerly awaited.