A self-cleaning composite deck drain apparatus which includes a removable top part having a top grating surface for receiving waste liquid and a trap for catching particulate matter from the liquid at a lower end. The drain apparatus further includes a bottom part having a drainpipe within an annular chamber formed thereabout for receiving and holding the top part. Circumferentially spaced locking tabs are affixed to the edge of the top part below the grating surface thereof for reception within tab receivers in the bottom part when the top part is inserted into the chamber of the bottom part and turned for locking of the tabs within the tab receivers. The top part includes a threaded bore within which a valve is manually operable to open and close the drainpipe. The deck drain apparatus is made of composite plastic materials to resist corrosion.