אורח חיים שע״זOrach Chayim 377

Se’if 1א׳

שְׁתֵּי עֲלִיּוֹת הַפְּתוּחוֹת לְחָצֵר זוֹ כְּנֶגֶד זוֹ, וְאַחַת עָשְׂתָה גּוּמָא בֶּחָצֵר כְּדֵי לִשְׁפֹּךְ בֶּחָצֵר שֶׁאֵין בָּהּ ד' אַמּוֹת מֵימֶיהָ וְהַשְּׁנִיָּה לֹא עָשְׂתָה, אִם עֵרְבוּ יַחַד שְׁתֵּיהֶם מֻתָּרוֹת לִשְׁפֹּךְ מִימֵיהֶן; וְאִם לֹא עֵרְבוּ יַחַד, וְהָאַחַת עֵרְבָה לְעַצְמָהּ וְהַשְּׁנִיָּה לֹא עֵרְבָה כְּלָל, זוֹ שֶׁלֹּא עֵרְבָה, אֲסוּרָה; וְשֶׁעֵרְבָה, מֻתֶּרֶת; וּבִלְבַד שֶׁלֹּא תִּשְׁפֹּךְ לְהֶדְיָא בַּגּוּמָא אֶלָּא תִּשְׁפֹּךְ בָּעֲלִיָּה וְהֵם יוֹרְדִים לַגּוּמָא. הַגָּה: דְּכֹחוֹ בְּחָצֵר שֶׁאֵינָהּ מְעֹרֶבֶת, שָׁרֵי (טוּר). וְהוּא הַדִּין אִם הֶחָצֵר יוֹתֵר מִד' אַמּוֹת, דִּשְׁתֵּיהֶם מֻתָּרִים בִּכְהַאי גַּוְנָא וְאֵין צְרִיכִים לְגוּמָא (בֵּית יוֹסֵף).

Two upper storeys that open onto a courtyard, one over against the other, and one of them made a pit in the courtyard — a courtyard that has not four cubits — to pour its water into, and the second did not make one: if they made an eruv (the loaf set aside to join separate households into one for the Sabbath) together, both are permitted to pour out their water; and if they did not make an eruv together, but the one made an eruv for itself and the second made no eruv at all, the one that made no eruv is forbidden and the one that made an eruv is permitted — provided that it does not pour straight into the pit, but pours in the upper storey and the water runs down into the pit. Hagah [Rema]: For the force of his act in a courtyard that has no eruv is permitted (Tur). And the same law applies if the courtyard is more than four cubits: both are permitted in such a case, and they need no pit (Beit Yosef).