So added water and got:

2014-05-31 13.27.26.jpg2014-05-31 13.27.34.jpg

And clearly the tone changes.

Video posted here of filling the container. http://youtu.be/YpQnxEugeLQ

So, there is a lot of noise. I might be able to lower the resistance value to see if the noise reduces. For some reason, the act of filling the container seems to change the tone, regardless of level. While water is pouring in, the tone changes, as the level goes up, that changed tone drops, then when the pouring stops the noise steps again. I don't know if the stirring of the water as the pour happens has anything to do with that.

If anyone can find me any good PC sound card signal analysis (e.g. frequency sampling tools) I can plot the changes against height of water.