Mishnayos Mikvaos Perek 4 Mishnah 1

המניח כלים תחת הצנור (one who puts vessels under the spout – which feeds a ritual bath) – a tube/spout (or a movable tube attached to the roof gutters) that rain waters enter through and descend through its mouth to the Mikveh/ritual bath. But here we are speaking of a wooden spout that was established and eventually hollowed out, for when it was established it did not have the law of a utensil upon it when it was detached.

ואחד כלים קטנים – that you should not say that they were not important (see also Tractate Kelim, Chapter 15, Mishnah 1).

אפילו כלי גללים – while they are not considered utensils with regard to ritual impurity, they are considered utensils to invalidate the Mikveh/ritual bath, even if he broke them or emptied them, for it is not similar to leaving jars/cannisters at the top of the roof to dry them out (see Tractate Mikvaot, Chapter 2, Mishnah 7).

ובית הלל מטהרין בשוכח – In the first chapter of Tractate Shabbat in the Gemara (16b), their dispute is established (i.e., between the Schools of Hillel and Shammai) concerning when he left them (i.e., utensils) under the spout at the time when the clouds were gathering and then they dispersed and he forgot them (i.e., the leaving of the utensils under the spout) and then the clouds gathered once again, that the School of Shammai holds that because of the dispersal of the clouds his first intention/thought process was not nullified, for he revealed his intention that he wanted that they (i.e., rain waters) would fall into them. But the School of Hillel holds that his intention/thought process was nullified, for when the clouds dispersed, his attention was diverted, for he held that rain would not fall any longer. But when he left them (i.e., the utensils) underneath the spout at the time of the gathering of the clouds, and the rains were late to come, and he went off to his work and forgot them, everyone holds that since ab initio, it was for this that he intended, his intention/thought process was not nullified through his forgetting. But if he left them (i.e., the utensils) at the time when the clouds dispersed, everyone holds that they are ritually pure, for he did not intend ab initio for this.

בשכח בחצר שהוא טהור – underneath the spout and it was filled from the dripping rain water and fell into the Mikveh/ritual bath. For specifically underneath the spout is where the School of Shammai disagrees, for he reveals his intention that he wanted that [the rain waters] would fall into them, but because of the dispersal [of the clouds], the first thought was not nullified. But if he leaves it in the courtyard [but not under the spout], even at the time when the gathering [of the clouds], it was not proven ab initio that his first pattern of thinking/intention was best, therefore, it (i.e., his thought) was nullified when they (i.e., the clouds) dispersed.

עדיין מחלוקת במקומה עומדת – it did not stand for a vote and the students of the School of Shammai were not greater [than those of the School of Hillel].