The victory achieved by successfully swatting an annoying fly can quickly be sullied by the resulting stain the fly's remains leave on the wall, table or window. Flies can vary in size but they all tend to leave black marks in the areas where they were squished and these marks should be cleaned immediately to maximize the odds of complete removal. Removing fly stains can be done in seconds with the proper cleaning tools.
Fill a spray bottle with three parts warm water and one part white vinegar. White vinegar is an effective cleaning agent on almost any surface and the water dilutes it to prevent damage.
Spray the fly stain with the vinegar solution. A small amount should work fine and you don't want to saturate surfaces such as wood or drywall.
Wipe away the fly stain with a cloth or paper towel. Respray the surface as necessary to remove any remaining discoloration.