Plumbing outlet boxes, such as for connecting washing machines, ice makers, and other plumbed appliances to plumbing systems, are provided that can be attached to each other in an assembly via a bracket. The plumbing outlet boxes may include one or more connectors. The assembly may further include a bracket having a plurality of engaging portions for engaging the connectors of the plumbing outlet boxes. The bracket may engage the plumbing outlet boxes to each other and/or to a stud within a wall.