These days, it probably makes more sense to throw away old paint brushes that have hardened latex paint on them - as in "I got so busy putting away the tools that I forgot to wash the brush". However, out of idle curiousity, what is the best way to clean such a brush. On the web, I find advice to soak it in warm soapy water (I don't believe that) or isopropyl alcohol (I'd probably have to buy laquer thinner to get pure isopropyl alcohol; the grocery store type of alcohol is part ethyl aclochol) or vinegar (that would suit me).

What's really best?