A better solution is to install a Teflon sensor well with a capacitive proximity sensor inserted in it. Cleaning is much easier with this setup because materials don't adhere to Teflon. Another method is to use conductive level probes. This is very precise but can only be used for conductive liquids. It also requires extensive alteration of the tank's top and an additional remote liquid level amplifier.
Conductive probes are also the most expensive.
Other approaches include photoelectric sensors or ultrasonic controls with analog outputs. These methods aren't very precise and need analog converters to obtain digital outputs when the desired levels are reached. There's also a new solution that has the advantages of Teflon, but only requires a small opening at the top of the tank. Precise and inexpensive, this device combines a photoelectric method with visible light fiber optic controls. Two plastic fiber optic cables are inserted into a Teflon tube that has a sensing end shaped in the form of a prism.