I keep a small stainless wire brush with my painting kit. this is just a little one a bit like a tooth brush. I use it to brush out little bits of paint that gets up near the ferrule. I use very warm water as it tens to soften the dried paint..that and a bit of laundry soap, dish soap can work too...it just depends where I'm washing in my home its the kitchen sink...in many of my clients homes it is in the laundry room utility sink.
Thank you kms I have had it sitting in warm soapy water but ther paint is not coming out I let it sit a bit too long before I got it in the soapy water.it is just I didn't want to ruin the brush and didn't know if I can just clean with mineral spirits on this brush for it is very expensive . I will try with the spirits thank you !
If the paint has dried, saturate it with Dawn Power Dissolver (available at Walmart). Then, wrap it tightly in a plastic bag and allow it to sit for a day. Then, if necessary, the wire brush or a nylon bristled nail brush should do the trick.
If the brush is synthetic, I would not use the mineral spirits. . . that is for solvent based paints.