Fill a sink with warm, soapy water.
Scrub the metal drinking bottle on the inside and outside using the bottle brush. Wash the bottle in the sink, periodically using the flashlight as necessary to check the interior for mold spots. Pay particular attention to the crevices in the lid and the bottom. Use a rolled towel if you don't have a bottle brush.
Rinse the bottle with clean water. Repeat steps two and three if you spot any more mold.
Rinse the metal drinking bottle with vinegar, inside and out. This will help kill any remaining mold spores.
Pour out the vinegar in the sink, and rinse the bottle with water again.
Dry the outside of the bottle and set it upside down overnight to allow the water inside to air dry.