Here is a schematic circuit diagram for my (as yet untested) water tank level meter. I offer no guarantee whatever that it will be any good, although I got a prototype working at home using a jug of water!
My diagram is probably unconventional in electronics terms. I am a self taught amateur!
The 4066 IC is basically just 4 switches each triggered by a separate signal. Mine cost 40p from Bitsbox.
You need to construct a kind of dipstick carrying the blue and red wires to their required depths and than connect it to the rest of the circuit accordingly. You may need to play with the resistor values R5-8 to get it to work properly. I will post what I find out as I progress with prototypes.
Version 1: 24 April 2012