When you have difficult to know the level of water in the tank you can use this circuit. It will indicate the level of water so you could see the level of water without looking into the tank.
This circuit constructed with transistor A1015, it is a PNP plastic encapsulated transistor. Use different height of insulator removed wire as shown in the circuit diagram.
|1.||Transistor PNP A1015||3|
Data sheet you can get A1015 datasheet here…