Eiruvin 7:6-7

Eiruvin 7:6

Here’s how the residents of an alley combine using a shittuf: one resident places a barrel (of wine, oil, etc.) and says that it belongs to all the residents. He grants them possession through a grown son or daughter, through a male or female Jewish servant, or through his wife (all of whom have independent agency). He may not grant possession through a minor son or daughter or through a non-Jewish servant as these do not have halachic agency, so it is as if he did it himself (and the process requires transfer to another person).

Eiruvin 7:7

If the food in the shittuf decreased below the necessary amount (which will be seen in the next mishna), he adds more and again grants possession; the other residents need not be informed of this. If the number of residents increased (requiring that more food be added), he adds and grants possession, and he must inform them.