Wikipedia does not seem to have an entry for hydraulophone (although they do define hydraulist - one who plays a hydraulophone). Apparently it's some kind of instrument that, when used to play the Hatikva, sounds incredible:

Knowing is half the battle.

References:
* Hatikva on Hydraulophone [hydraulist / YouTube]

Previously:
* Tuesday WTF - Japanese Tourists Singing At the Kotel [Video]
* Shabbat Beauty - Blossoming In Israel
* Tuesday Hatikva - Shiri Maimon Gets People Emotional [Video]