The frame that houses the drawer hinges on the rear top edge using bolts mounted to wooden fixings attached to the underside of the bench. Restrained by short chains, the frame hinges far enough to allow the front to drop below the frame rail. When pushed up under the bench the frame is held in place by a rotating wooden toggle on each side that bear against a sloped block attached to each side of the frame. As the toggles are rotated against the blocks the frame is tightened into the underside of the bench top.
Standard ball-bearing drawer slides are used to allow the drawer to move freely and also have a retaining lock when the drawer is pushed fully closed. A lining of anti-slip material prevents items sliding in the drawer (in practice the slope on the open drawer is so shallow that things stay put in any case). We've posted a short video of the drawer on our Instagram feed.