A fitting for plumbing systems, such as drain/waste/ventilation (DWV) systems that is chemically and mechanically joinable is described. A socket of the fitting has an interior surface configured for chemically joining with tubing. An exterior surface of the socket includes a plurality of projections extending radially outward therefrom. A collar that includes a sidewall with a plurality of bayonet-style channels configured to engage respective projections is provided. Interaction of the projections with the channels during rotation of the collar with respect to the fitting draws the collar toward the fitting and compresses an O-ring between the collar, socket, and tubing inserted therein to form a fluid-tight seal and/or mechanically couple the tubing in the socket. The collar may include longitudinally depending flanges that are depressed against the tubing by a compression ring to mechanically couple the tubing in the socket.