#3 Use vinegar & hot water to clean paintbrushes. Fill a small bowl with 1/2 vinegar, 1/2 hot water, soak for 30 minutes. If you have a brush that's really dirty and has dried paint on it, put your brush in a small pot and cover the bristles in vinegar. Bring the vinegar to a boil and let simmer for a few minutes. Remove the pan from the heat and let it cool before you remove the brush. Once it's cool, wash it with water and you should be able to gently clean all the paint off really easily.