Gemara

18a (Mishnah): We distance soaking water (of flax) from vegetables, and leeks from onions, and mustard from bees.

(Mishnah and Beraisa - R. Yosi): One may plant mustard near his neighbor's bees. He can say 'rather than tell me to distance my mustard, distance your bees, for they eat the stems of my mustard plants!'

Question: If one must distance damagers from the border, both of them must distance themselves!

Answer (Rav Papa): When Reuven set up the soaking pit, leeks or mustard, he owned the adjacent field. Later, he sold it.

Question: If so, why do Chachamim say that he must distance himself? Also, why does R. Yosi agree about water and leeks?

22b (Rav Ashi): R. Yosi admits regarding Giri ('arrows', i.e. damage that comes directly from the person's hand);

25b (Mishnah): Reuven must distance his tree 25 Amos from Shimon's pit. If the tree was there before the pit, he may not cut the tree.

R. Yosi says, even if the pit preceded the tree, he may not cut it. Just like Shimon may dig in his own property, Reuven may plant in his own property!

64a (Mishnah - R. Akiva): If Reuven sold his house to Shimon; Shimon does not acquire the pit and cistern. (If Reuven wants to use them,) he must buy the rights to a path to them.

Chachamim say, (he may use them, and) he need not buy a path.

Suggestion: R. Akiva holds that one sells generously (he does not retain a path for himself), and Chachamim hold that one sells stingily.

Rishonim

Rif (13b): We establish the Mishnah (of bees) when one bought half the field.

Rebuttal (Rosh 2:3): It is unreasonable to obligate one to distance his mustard if he was allowed to plant it! This is like a tree (one may keep it if it preceded the pit). Rather, the text says that Rav Papa's answer was rejected.

Rambam (Hilchos Shechenim 2:12): If two bought a field from one seller, neither has any rights in the other's portion. He may seal the windows.

Rosh (1:20): The Ri says that if partners divided and received houses, one may build a wall even if it diminishes the light of the other's house. Even according to the Ri, if the only window of each house overlooks the other's property, surely they did not intend to get dark, useless houses.

Taz (CM 154:28): The Rosh says so only about partners who divide, but if one sold to two, we are not concerned if the house will not have any light.

Nimukei Yosef (13a DH Masnisin (2), citing R. Yonah): Because R. Yosi agrees about Giri, if one bought a house with a window overlooking the seller's Chatzer, he must seal the window. Even though the window was made with permission, and even though we hold that one sells generously, one does not acquire rights to damage. Regarding the damages in the Mishnah (25b), if the seller put them near a wall and sold the Chatzer with the damager, the buyer need not distance the damager. He did not put it close! Hezek Re'iyah (loss of privacy) is different, for he constantly damages through looking. This is when there was damage at the time of the sale. If one sold a house with a window overlooking a ruin, and later the seller built the ruin, the buyer need not close his window. This is like the Mishnah (25b) says, that if a tree preceded the pit, we do not cut the tree.

Poskim

Shulchan Aruch (CM 154:28): If Reuven gave or sold at the same time a house to Shimon and the Chatzer to Levi, and there were windows in the house open to the Chatzer, Levi may build in front of them. Likewise, if he gave or sold the Chatzer to Levi and kept the house for himself, Levi may build in front of the windows (Rema - some say that he cannot build) unless he distances four Amos.

Beis Yosef (DH Kosav Rabeinu): R. Yerucham (31:6 191b) says regarding a soaking pit near a vegetable patch that the seller must distance himself, even if the damage was there at the time of the sale. If so, if one had a house with a window overlooking a Chatzer, and he sold the Chatzer, he must close the window. Even R. Yosi, who says that the victim must distance himself, agrees regarding Giri that the damager must distance himself. One sells generously. Some say that the same applies when two bought from one seller. Some disagree.

SMA (65): When he gave or sold at once, all agree that Levi may build in front of the windows. Meforshim argue about when he sold one after the other, which is like when he sold the Chatzer and kept the house. He sold all his rights.

Beis Yosef (DH Kosav ha'Rivash): The Rivash (517) says that if Yakov sold a house to Reuven, and later sold the roof to Levi, and Reuven objects to rainwater that flows off the roof, he can say that Yakov sold all his rights in the house. Surely, one sells generously. However, all Meforshim agree that Reuven cannot force Levi to remove the damage. Rather, Reuven may build in his property what is needed to prevent damage to himself. Likewise, when we say that David does not have window rights against Aharon, it means that he cannot stop Aharon from building within four Amos of David's window, lest he block the light. Aharon may build anywhere on his property, but he cannot force David to close his window to prevent Hezek Re'iyah. However, the Rambam says that he can force David to close his window, because Hezek Re'iyah is Giri. Dripping rainwater is not Giri. It is from Shamayim. Reuven may stop up the drain pipe if it is in his Reshus, but Levi is not responsible if this causes damage to the Reuven's roof. Levi just needs to fix it like anyone else who owns an Aliyah roof over another's house.

SMA (66): The Mechaber (Sa'if 27) holds that Levi cannot force Shimon to close the windows. The Rema there brought that some say that he can force him.

Rema: If one sold a house and kept the Chatzer for himself, some say that he cannot seal the windows, for one sells generously. The same applies to one who gives. Some disagree. See 155:25

Beis Yosef (DH Kosav ha'Rashba): A case occurred in which Yakov sold a house and kept a garden for himself. Shimon later bought the garden, and claimed that surely Yakov did not sell in a way that leaves Hezek Re'iyah for the garden (i.e. if the buyer has rights to have windows from which he can see in). The Rashba (3:161) said that if windows from the house were open to the garden and Yakov sold the garden, surely he did not keep window rights, for one sells generously. However, when he sold the house and kept the garden, one could say that since the windows were opened with permission, and one sells generously, he sold window rights. However, my Rebbi, R. Yonah, agreed that even if he sold the house and kept the garden, he did not sell window rights. We hold that regarding damage of Giri, the damager must distance himself. Hezek Re'iyah is Giri. Presumably, he sold on condition to remove the windows. A person does not sell damage (to himself) of Giri!

Taz: Why do some say that he cannot build? One sells generously! We must say that this is like Tosfos (the Ri in the Rosh above), and we discuss closing the only window.

Rema (155:25): If Reuven sold his house to Levi and his garden to Moshe, Moshe need not distance his trees even if Reuven sold the house first. We do not say that one sells generously.

SMA (61): Even though the roots of the trees go under the walls of the house and harm it, the Halachah follows R. Yosi who allows one to plant in his own Reshus.

SMA (62): He need not teach about trees that were already planted. Moshe bought them just like they were Muchzak to Reuven. Rather, Moshe may plant new trees.

Rema: See above 154:28.

SMA (63): There, the Rema cites an opinion that if one sold a house and kept the Chatzer for himself, he cannot seal the windows, for one sells generously. There is different, for to (build and thereby) seal windows overtly damages now. Planting does not damage, just the roots that come later damage.