Reference for Tahorot 10:7
הַזּוֹלֵף אֶת הַבּוֹר, נִמְצָא שֶׁרֶץ בָּרִאשׁוֹנָה, כֻּלָּן טְמֵאוֹת. בָּאַחֲרוֹנָה, הִיא טְמֵאָה וְכֻלָּן טְהוֹרוֹת. אֵימָתַי, בִּזְמַן שֶׁהוּא זוֹלֵף בְּכָל אַחַת וְאַחַת. אֲבָל אִם הָיָה זוֹלֵף בְּמַחַץ, נִמְצָא שֶׁרֶץ בְּאַחַת מֵהֶן, הִיא טְמֵאָה בִּלְבָד. אֵימָתַי, בִּזְמַן שֶׁהוּא בוֹדֵק וְלֹא מְכַסֶּה אוֹ מְכַסֶּה וְלֹא בוֹדֵק. הָיָה בוֹדֵק וּמְכַסֶּה, וְנִמְצָא שֶׁרֶץ, בֶּחָבִית, הַכֹּל טָמֵא. בַּבּוֹר, הַכֹּל טָמֵא. בַּמַּחַץ, הַכֹּל טָמֵא:
If one empties a pit [of wine into barrels], and a vermin was found in the first [barrel he filled], they are all impure. If [it was found] in the last one [he filled], it is impure and all the rest are pure. When is this the case? When he empties into each one individually. But if he was emptying with a ladle, if a vermin was found in one of them, that one alone is impure. When is this the case? When he inspects [each barrel, before emptying wine into it] but does not cover [each one after emptying in the wine], or he covers [each barrel] but does not inspect. If he was inspecting [each one] and then covering, and a vermin was found in one of the barrels, everything is impure; if [it was found] in the pit, everything is impure; if [it was found] in the ladle, everything is impure.