MB4 246a: Shared Yard Between Two Balconies (377:1)

Water can be poured into your yard more if it's larger than 4 square amot. If the yard is less than 4 square amot, water can only be poured into the yard if there is a pit in the yard.

If 2 balconies open into a yard but the owners didn't make a joint eruv, when can they empty water into a pit in the courtyard?