This device is extremely reliable (as long as it's not sewage which tends to coat the optics!) and is actually manufactured by Honeywell Microswitch in the USA. Connect with minimal components directly to your PIC (or even Relay).

http://docs-europe.electrocomponents...6b8001adaf.pdf

It is a little power-hungry for Battery applications though.

You don't have to go Stainless Steel if you use AC exitation on your probes... PWM say a 1kHz signal to one probe (via a 100nF Capacitor, the other probe (again via a 100nF) can be used to detect the signal returning. To minimise power consumption, turn the PIC on only every few seconds (typical Rain Detector application to alert you to take the washing indoors).