Reference for Eduyot 7:4
הֵעִיד רַבִּי צָדוֹק עַל זוֹחֲלִין שֶׁקִּלְּחָן בַּעֲלֵה אֱגוֹז, שֶׁהֵן כְּשֵׁרִים. מַעֲשֶׂה הָיָה בְאָהֳלְיָא, וּבָא מַעֲשֶׂה לִפְנֵי לִשְׁכַּת הַגָּזִית, וְהִכְשִׁירוּהוּ:
R. Tzaddok testified — that they are kosher — about zochalin which were made to jet through the leaf of a nut [i.e., the outer shell of a nut, the green shell. If, when it was moist, he made it like a tube through which the zochalim would run and jet outside of it, the jetted waters are halachically zochalim, and they are kosher for the waters of purification (the red heifer), and the immersion of zavim. And we do not say that since they entered through this shell, which acts as a receptacle through which they are jetted out, they are not halachically zochalin — for that shell is not considered a vessel.] This once happened in Ahalya, and it came before the lishkath hagazith (the seat of the Great Sanhedrin in Jerusalem), and they ruled it kosher.