John,
Thanks for pointing to my circuit. I would have done that earlier, but Sam's original spec's (8v battery and a darlington) almost sounded like a school assignment.
Sam,
My circuit was to monitor for an empty plastic fuel line from an aircraft's overhead fuel tank. It could also be used with a plastic "sight tube" outside a container. I just measured some kerosene and naphtha, and got infinite resistance. So, it looks like it's possible to just use two metal probeds directly in the fuel container. Since capacitive sensors are affected by their surroundings, can you describe in detail were and how this "plastic container" is used?
Ken