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 without the use of separate connectors or mounting brackets. In particular, plumbing outlet boxes are described that include receiving features and mounting tabs extending outwardly from the side walls. The receiving features and mounting tabs are arranged such that the plumbing outlet box has rotational symmetry. In this way, receiving features may be engaged with mounting tabs of an adjacent plumbing outlet box regardless of the relative orientation of the mating plumbing outlet boxes.