Eiruvin 8:9-10

Eiruvin 8:9

If a courtyard is smaller than four cubits by four cubits (about 6’x6’), one may not pour water out there on Shabbos unless they first built a pit that would hold two seah (about 7 gallons) below the overflow hole. This pit can be inside or outside the courtyard, though if it is made outside the courtyard, it must be covered (to keep it from appearing to be part of the public domain). Inside the courtyard this is not a concern, so the pit need not be covered.

Eiruvin 8:10

Rabbi Eliezer ben Yaakov says that if a channel of waste water continues from the courtyard into the public domain, where it is covered for four cubits (about six feet), then one may pour water into it on Shabbos. The Sages say that even if a roof or a courtyard is 100 cubits long (about 150 feet), one may not pour water into this channel of waste water. Rather, he may pour it onto the roof and let it flow down to the channel on its own. The courtyard and its gazebo combine to form four cubits (for the purposes of the four cubits by four cubits mentioned in 8:9).