Thanks for the reply Zep!
Well, I'm going to have to check more now. I did take the leads off the sensors to do my testing, and the screws are only about 1/4 inch long and I think they are brass. They screw into some sort of metal thread...but the tank is empty, so I don't know if they are indeed the actual sensor touching water. More pictures and investigations to come.
BTW, I was trying to do more searching on the subject, and amazingly enough, my grey and black water sensors work perfectly! Although I'd give up both for the freshwater sensors to work.