In a gentle, repetitive motion, push the brush up and down under the running water, pushing and pulling the bristles together and apart. This motion, combined with the running water, will help the bristles shed themselves of any wet paint. Total cleaning time could take anywhere from 5 to 10 minutes, so expect to put in a little sweat.
You’ll know the brush is clean when clear water runs out from the bristles as you push it up and down. Remember not to be too forceful; you only want to bend the bristles in a natural direction. Too much force can unnaturally bend, and sometimes break, the brush hairs.