Gather all your ingredients and tools. Ensure you have a clean, airtight container ready for storage.
In a clean bowl or directly in your storage bottle, combine 1 cup of distilled water with 2 tablespoons of baking soda. Stir or whisk gently until the baking soda is mostly dissolved. A few undissolved particles are okay.
Add 1 tablespoon of the generic liquid antacid to the mixture. Stir or whisk again until well combined.
Finally, add 1 teaspoon of the generic diphenhydramine liquid. Mix thoroughly until all components are evenly distributed.
Pour the mixture into your airtight storage bottle. Gently shake before each use.
This mixture is now ready to be used as a soothing mouth rinse.