Immerse the metal object in a solution of equal parts white vinegar and warm water and let it soak for 20 minutes. If you cannot immerse the object, spray the surface with undiluted white vinegar and wait 20 minutes.
Sprinkle baking soda over the greasy area.
Wet a scrub brush with white vinegar and add a few drops of liquid dish soap to the brush's bristles.
Scrub the metal surface with the brush. The vinegar should have already dissolved much of the grease. The baking soda will help remove the grease and also acts as a mild abrasive.
Rinse the metal thoroughly and allow it to air dry.