Abstract: Improved outlet boxes are provided for installation in a wall to connect water supply lines and drain lines to the corresponding lines from an appliance. Molded plastic outlet boxes having dual drains; left-to-right reversibility; adaptability to multiple drain and inlet line configurations, including top, bottom and side inlets; inclined bottom walls with gutters and removable webs facilitating drainage; and rear walls with recesses accommodating flushable water supply line connections are disclosed. Dual drain connectors adapted to combine the flows from dual drain outlets into a single drain pipe and knock-outs with downwardly extending, elongated tabs are also disclosed.