הָעוֹשֶׂה נֶקֶב שֶׁהוּא עָשׂוּי לְהַכְנִיס וּלְהוֹצִיא כְּגוֹן נֶקֶב שֶׁבְּלוּל הַתַּרְנְגוֹלִין שֶׁהוּא עָשׂוּי לְהַכְנִיס הָאוֹרָה וּלְהוֹצִיא הַהֶבֶל הֲרֵי זֶה חַיָּב מִשּׁוּם מַכֶּה בְּפַטִּישׁ. לְפִיכָךְ גָּזְרוּ עַל כָּל נֶקֶב אֲפִלּוּ הָיָה עָשׂוּי לְהוֹצִיא בִּלְבַד אוֹ לְהַכְנִיס בִּלְבַד שֶׁמָּא יָבוֹא לַעֲשׂוֹת נֶקֶב שֶׁחַיָּבִין עָלָיו. וּמִפְּנֵי זֶה אֵין נוֹקְבִין בְּחָבִית נֶקֶב חָדָשׁ וְאֵין מוֹסִיפִין בּוֹ. אֲבָל פּוֹתְחִין נֶקֶב יָשָׁן. וְהוּא שֶׁלֹּא יִהְיֶה הַנֶּקֶב לְמַטָּה מִן הַשְּׁמָרִים שֶׁאִם הָיָה לְמַטָּה מִן הַשְּׁמָרִים הֲרֵי זֶה עָשׂוּי לְחַזֵּק וְאָסוּר לְפָתְחוֹ:
A person who makes a hole that can be used as an entrance and as an exit - e.g., a hole in a chicken coop that is used to allow light to enter and to allow foul air to leave - is liable [for performing the forbidden labor] of dealing [the final] hammer blow. Accordingly, [the Sages instituted] a decree [forbidding] the opening of any hole, even one intended to be used only as an outlet or only as an inlet, lest one open a hole for which one is liable. For this reason, it is forbidden to make a new hole in a cask or to widen an existing one. One may, however, open an existing hole [that has been plugged]. [The above leniency applies] provided the hole is not located below the level of the dregs [in the cask], for a hole made below the level of the dregs is intended to hold fast. [Therefore,] it is forbidden to open it.
