I work in theatre and at the end of the day we sometimes don't have the energy to clean our rollers and brushes. 99% of the time we use water based paints. If we're leaving them, and it's always with a guilty conscience, we drench the bristles with the paint we're using and wrap them in plastic. But when we clean them, we clean them thoroghly until not a single drop of clour comes out of the bristles. Also, to spare your brushes when scrubbing them with the wire brushes, use only the stainless steel brushes on natural bristle brushes, when cleaning a brush made from artificial fibres, use a plastic scrub brush and it'll look like new when you're done.