Yerushalmi Eruvin 8:9 ירושלמי עירובין ח׳:ט׳

MISHNAH: If a courtyard be less that four [by four] cubits one may not pour water in it on the Sabbath unless one make for it a sump containing two seah below the hole²⁵Since the space is so small one has to assume that water poured into the courtyard will run off into the public domain. Then pouring the water may look as if one were pouring from a private into the public domain, which would look like a Sabbath violation. Therefore one requires that there be a sink absorbing 2 se’ah (about 25 l) of the run-off. If later there is an overflow from this sink it is not directly the result of pouring out water and therefore one may pour out water in unlimited amounts., whether inside or outside; only that outside one has to cover but inside one does not have to cover²⁶This makes the sink an extension of the courtyard; it no longer is counted as public domain.. Rebbi Eliezer ben Jacob says, one may pour water on the Sabbath into a sewer which is covered for four cubits in the public domain, but the Sages are saying, even from a roof or a courtyard 100 cubits [wide] one may not pour into the sewer²⁷Since it looks like pouring into the public domain. but one may pour onto the roof and it flows down into the sewer. Courtyard and porch combine for four cubits²⁸If the sum of the areas is at least 16 square cubits nothing has to be excavated..
Two rows of apartments²⁹Greek δίαιτα, ἡ. The two rows of houses share a common courtyard but no eruv., one opposite the other, one side made a sump, the other did not make a sump. Those who made a sump are permitted, those who did not make a sump are forbidden.

HALAKHAH: Paragraph¹³¹Discussion of Mishnah 10.. They estimated (the place of)¹³²Probably the word מקרם should be deleted. what a person uses is two se’ah and four cubits absorb two se’ah¹³³A person on one day uses no more than 2 se’ah of water and an unpaved area of 16 square cubits can absorb 2 se’ah per day. Babli 88a/b.. If the sump sprung a hole¹³⁴And then any additional water which is poured into the yard will immediately cause water to flow into the public domain., there are Tannaïm who state that one does not have to plug; there are Tannaïm who state that one has to plug. If the sump was full, there are Tannaïm who state that one has to empty, there are Tannaïm who state that one does not have to. Rebbi Mana said, it is one Tanna. He who says that one has to plug forbids to pour out¹³⁵He reads לשפוך as “to pour into the yard”. If it is necessary to plug the hole so that no water may flow from it into the public domain, it will be forbidden to pour anything into the yard for the rest of the day., he who says that one does not have to plug permits to pour out. Rehhi Ḥiyya bar Marius said to Rebbi Mana: So said your father Rebbi Jonah, thinking about it¹³⁶Reading בָּהּ for בר “outside”.: If it is sloping¹³⁷Greek καταφερής, -ές. inside, even more than ten is permitted¹³⁸Obviously this has to read “forbidden”. If the yard is on an incline, any water spilled there will immediately flow into the public domain. But if the outside is sloping into the courtyard, the water will remain in the yard.; outside even less than ten is permitted. What we are dealing with if it is level.

The Mishnah disagrees with Rebbi Joḥanan: “Courtyard and porch combine for four cubits²⁸If the sum of the areas is at least 16 square cubits nothing has to be excavated..” He explains it if they are level. A baraita disagrees with Rebbi Simeon ben Laqish: The terrace, the roof, and the courtyard combine for four cubits. Still it is if they are level. You should know that it is so since it was stated: The house, the upper floor, the courtyard, and the porch do not combine. Is that not because they are not level¹³⁹Since the disagreement between R. Joḥanan and R. Simeon ben Laqish is not indicated, it is difficult to assess the meaning of the discussion. An educated guess (by Qorban haEdah) is that R. Joḥanan holds that domains can be added only if they are on equal heights; the questioner assumed that the porch was higher than the courtyard. In the baraita quoted as opposing R. Simeon ben Laqish it is clear that courtyard and rooftop cannot be of equal height. It is conjectured that he holds that the list of the Mishnah, yard and porch, is exhaustive; this would exclude terrace and rooftop. The answer is that he accepts yard and everything on the same level, porch and everything on the same level. In this interpretation the baraita does not allow one to add the surface areas of courtyard and rooftop.?

Rebbi Jeremiah said, Rebbi Meïr and Rebbi Eliezer ben Jacob both said the same. Rebbi Eliezer ben Jacob as we have stated: “Rebbi Eliezer ben Jacob says, on the Sabbath one may pour water into a sewer which is covered for four cubits in the public domain, but the Sages are saying, even from a roof or a courtyard 100 cubits [wide] one may not pour into the sewer.” Rebbi Meïr as it was stated: In large cities one may pour water into flows even though they are perforated, the words of Rebbi Meïr¹⁴⁰If a river is diverted into many small currents which run in streets and through courtyards (as can be seen, e. g., in Freiburg i. B., Germany), one may pour water into them on the Sabbath since it will not be noticed.. ¹⁴¹The main discussion about prohibitions added because people may get a bad impression, which also includes the text here, is in Kilaim 9:2 (Notes 34–40, Eruvin problem Note 39). Rav’s opinion is accepted in the Babli (Šabbat 64b, 164b, Beṣah 9a, ˋAvodah zarah 12a) but consistently rejected in the Yerushalmi. And it was stated thus, if it was a drainpipe it is permitted; in the rainy season it is permitted¹⁴²Babli 88b. The Babli holds that during the rainy season there never was any rabbinic prohibition because everything is being wet anyhow.; streaming spouts are forbidden and Bar Qappara stated, if it occurred at a hidden place it is permitted. This disagrees with Rav and he cannot explain it, since Rav said that everything forbidden because of a bad impression is forbidden even in the most private room.