Yosef Karo, Translation:Shulchan Aruch — Orach Chaim 377…
“ If they did not make a joint eruv and one made an eruv for itself and the other made no eruv, the one that did not make an eruv is forbidden and the one that made in eruv is permitted, as long as it does not pour directly to the pit but rather pours on the upper chamber and the water falls into the pit. Rem"a: Because we permit [things falling] by their own strength in a yard without an eruv (Tur. This is also the rule for a yard with four amot; both are permitted such a scenario and they need no pit (Beit Yosef) . ”
