Dettol is well known as a very effective stripper of acrylic paint. Its active ingredient is chloroxylenol, which breaks down the acyrlic medium and allows paint to be removed from miniatures.
I've just discovered that it's also quite an effective brush cleaner as well. Late last year I bought some Winsor and Newton kolinsky sable brushes, and to my great shame they have quickly become clogged with paint (I am not especially diligent in cleaning my brushes after use). Yesterday afternoon, as an experiment I put one of these brushes into some Dettol along with some other miniatures.
This morning I took it out of the Dettol, rinsed it out and gave the bristles a quick rub with some handwash (any liquid detergent would also work). The bristles are pretty much back to normal, with no paint clogged up at the ferrule.
So if your brushes are looking a little tired, and you don't want to fork out for new brushes or brush cleaner, then Dettol may be the ideal alternative.