The pilot was undergoing a ninety day flight check. On the downwind leg of the second circuit when the landing gear was selected down, the nosegear extended and locked but both maingear legs remained retracted. Attempts to manually pump the maingear down were unsuccessful and the nosegear could not be retracted. The instructor landed the aircraft on the grass with the nosegear extended and the maingear retracted. Subsequent investigation revealed the aircraft hydraulic system had suffered a total fluid loss. The loss occurred from a hole in a hydraulic down line caused by abrasion from a rudder cable fork end.