The drain plug is on the bottom of the rotor casing. tilt the mower to one side, ensuring the air filter is on the topside(this is important or you will contaminate the filter). Scrape away the old grass debris around the rotor shaft. you will see a drain plug. Its a Briggs and Stratton engine so they vary but a 1/2 inch socket drive will usually undo them. (anti-clockwise) \bout the size of a 5p piece.
Mo, August 2007