Mishnah Mikvaos 4:1: If one places vessels under a [drain] pipe, whether they are large vessels or whether they are small vessels, or even vessels made from feces, stone vessels, or earthen vessels, [if rainwater flowed through the pipe and into them] they invalidate a mikveh [a gathering of water collected by natural means and immersed in for purification; if the waters flow through these vessels and into a mikveh they invalidate it, since they are considered drawn waters]. Whether one places them [under the drainpipe] or forgets them, [this still applies,] according to Beit Shammai. And Beit Hillel consider it pure [i.e. the waters do not render a mikveh invalid from being able to purify] in the case of one who forgets. Rabbi Meir says: they voted [on this matter], and Beit Shammai had the majority over Beit Hillel. And they [Beit Shammai] agree in case of one who forgets [vessels] in a courtyard, that it [a mikveh into which rainwater from those vessels was poured] is pure. Rabbi Yose says: the disagreement still stands in its place.

הַמַּנִּיחַ כֵּלִים תַּחַת הַצִּנּוֹר, אֶחָד כֵּלִים גְּדוֹלִים וְאֶחָד כֵּלִים קְטַנִּים, אֲפִלּוּ כְלֵי גְלָלִים, כְּלֵי אֲבָנִים, כְּלֵי אֲדָמָה, פּוֹסְלִין אֶת הַמִּקְוֶה. אֶחָד הַמַּנִּיחַ וְאֶחָד הַשּׁוֹכֵחַ, כְּדִבְרֵי בֵית שַׁמַּאי. וּבֵית הִלֵּל מְטַהֲרִין בְּשׁוֹכֵחַ. אָמַר רַבִּי מֵאִיר, נִמְנוּ וְרַבּוּ בֵית שַׁמַּאי עַל בֵּית הִלֵּל. וּמוֹדִים בְּשׁוֹכֵחַ בֶּחָצֵר שֶׁהוּא טָהוֹר. אָמַר רַבִּי יוֹסֵי, עֲדַיִין מַחֲלֹקֶת בִּמְקוֹמָהּ עוֹמָדֶת:

Mishnah Mikvaos 4:2: One who places a board under a [drain] pipe, if it [the board] has a rim, it renders a mikveh invalid; and if not, it does not render a mikveh invalid. If one stood it up [the board] to be rinsed [under the drainpipe], either way [whether or not it has a rim] it does not render a mikveh invalid.

הַמַּנִּיחַ טַבְלָא תַּחַת הַצִּנּוֹר, אִם יֶשׁ לָהּ לְבִזְבֵּז, פּוֹסֶלֶת אֶת הַמִּקְוֶה. וְאִם לָאו, אֵינָהּ פּוֹסֶלֶת אֶת הַמִּקְוֶה. זְקָפָהּ לִדּוֹחַ, בֵּין כָּךְ וּבֵין כָּךְ אֵינָהּ פּוֹסֶלֶת אֶת הַמִּקְוֶה: