The most effective and economical/environmentally friendly way I have recently found is to use a flat tin like Cafe Creme small cigars come in, pour in only a small amount of thinners/brushwash/acetone, to a depth of about 2mm. Holding the brush firmly push it down against the base at an angle whilst rotating the handle, this will very quickly clean all the fibres leaving only a small residue in the ferrule which once dry will prevent hair loss next time you use it. Quick wipe with a kitchen towel and done. Dispose of the residue using the same towel, leave it to evaporate.