No, I tried water but it reduces the resonance. The sound does not come from the difference in the volumn of air, but from the resonance of the side of the bottle. The three bottles I do have, difer only in the thickness of the walls, and the number of rings on the sides. I know this sounds crazy, but you actually have to hear it to understand... Think of something that goes OMMMMMM as you strike it, but again, only with a rather soft tipper.

And it sounds like Hardi is on the Claymore 12 Step Program... you must stay within 12 steps of the toilet at all times... Good Luck!