Listerine Cool Mint Mouthwash (250ml). Minty germ-fighting boldness! Just 30 seconds of rinsing, twice a day. That’s all it takes when you use LISTERINE® Coolmint Mouthwash.. Used twice a day LISTERINE® Cool Mint is proven to:. 1. Kill germs: Kills up to 97% of germs left behind after brushing. 2. Reduce plaque: By up to 56% more than brushing alone. 3. Maintain fresh breath: Provides lasting fresh breath confidence. 4. Maintain healthy gums: Kills germs above and below the gum line to keep gums healthy