Bava Basra, Chapter 4, Mishnah 2. This Mishnah is a direct continuation of the previous one, dealing with the following scenario: someone sells his house to another person generally, without specifying what is included in the sale - what enters into the sale and what remains in the seller's possession.
"Lo es habor velo es hadus" - not the cistern and not the vat:
Bor - a cavity dug into the ground, such as a reservoir collecting water in the basement of the house.
Dus - a reservoir built above ground.
Both of these are intended for storing water. Since not every house needs its own water reservoir, and people usually relied on a more public source - the well or the shared cistern for all members of the courtyard - an independent storage facility, whether below or above ground, is not considered an essential part of the house. Therefore, the seller did not intend to include it in the sale, and even though access to it is through the basement of the house and its entrance (which we will discuss below) - it is not sold with the house.
"Af al pi shekasav lo umka veruma" - even though he wrote for him the depth and the height:
This law applies even when the bill of sale specified not only the house, but also "umka" - its depth, and "ruma" - its height. Even then, the sale does not include an underground cistern in the basement, as this is not what the seller intended. His intention with the phrase "umka veruma" is regarding building rights: the permission to build an additional floor above the house - "ruma", and the permission to dig deeper into the ground - "umka". This does not include independent structures, such as a water cistern, even though they are located in the ground.
The Gemara says: If he wrote for him in the document "knei lach mis'hom araa ve'ad rum rakia" - meaning, a sale that extends from the depths of the earth to the heights of the sky - this specification comes to include everything found within the ground, including the cistern. But without this wording, the cistern is not included in the sale.
"Vetzarich likach lo derech" - and he must purchase a path for himself - when the seller retains the cistern for himself:
When someone sells his house and retains the rights to the cistern in the basement for himself, the Tanna'im disagree as to whether he also acquired the right of access to it:
Rabbi Akiva - "tzarich likach lo derech": According to his view, a person sells with a "good eye," meaning with a generous spirit, without retaining additional rights for himself. The house was sold in its entirety and no rights of passage were kept for the seller, and therefore he has no permission to access the cistern in the basement - even though the cistern is his - unless he reaches a financial arrangement with the new owner, who will permit him entry on days and under conditions agreed upon between them in exchange for payment.
The Sages - "eino tzarich likach lo derech": According to their view, a person sells with a "bad eye," meaning he minimizes the scope of the rights he gives up. Since he intended to retain the cistern in the basement for himself, he also retained the rights of access to it, and he did not sell those with the house. Therefore, he does not need an additional financial arrangement, and he may access the cistern within the limits of reason (the definition of these limits is not discussed here).
The halachah follows Rabbi Akiva, that a person sells with a "good eye" - and this principle works in both directions, as will be explained.
"Umodeh Rabbi Akiva bizman she'amar lo chutz me'eilu" - and Rabbi Akiva concedes when he says to him, "except for these":
If the seller explicitly stipulated that he is selling the house but not the cistern, even Rabbi Akiva concedes "she'ein tzarich likach lo derech" - he does not need to purchase a path for himself. There is no need for a separate financial arrangement for access to the cistern in the basement, since his very statement, "I am not selling you the cistern," clearly establishes that he intends to retain the right of access to it for himself.
"Machran le'acher" - if he sold them to someone else:
The Mishnah also discusses the opposite scenario: The homeowner does not sell his house, but rather sells only the cistern in the basement to someone else, and the only way to reach it is through the entrance of the house:
Rabbi Akiva - "eino tzarich likach lo derech" - he does not need to purchase a path for himself: A person sells generously, and the sale includes the accompanying rights. Once he sold the cistern, he sold with it the rights of access to it, even though the entry is through the entrance of the house (within reasonable limits). Thus, the buyer already possesses a monetary right to access the cistern, and no additional arrangement is required.
The Sages - "tzarich likach lo derech" - he must purchase a path for himself: A person sells stingily, retaining for himself as many rights as possible. The seller retained all access rights to the cistern, and therefore the buyer will be required to reach a financial arrangement with him in order to access the cistern he purchased.
In summary: The halachah follows Rabbi Akiva, that a person sells generously, and this principle works in both directions. One who sells the house and retains the cistern for himself - he sold the access rights along with the house, and he will be required to pay in order to access his own cistern. However, one who sells the cistern itself - he sold it together with the access rights, and the buyer is not required to pay in order to reach the cistern he bought.