More background, and I apologize if I'm not entirely correct but there used to be Shakuhachi songs that would be played between Samurai and monks to gain access to enemy strongholds. The guard would play a piece, then the Samurai would play the corresponding piece, thus gaining access with no bloodshed.
The bucket was used by zen monks who belonged to the Fuke sect. During many centuries to perform this kind of music with the shakuhachi was privative of religious music.
It was also to deter away from celebrating the monk therefore removing ego from the meditation. "Thus Fuke monks rarely chanted sutras or other Buddhist texts, but rather relied upon scores of sacred shakuhachi music called honkyoku to express and transmit awakening" en.wikipedia.org/wiki/Fuke-sh%C5%AB
