No, it is not necessary, except if the paint already hardens in the brush while working, then the drying process is already too far advanced. When you do clean the brushes beforehand, the gel does stay clean for a longer period of time. In addition, your brushes will remain in better condition when you clean them regularly with our Clean and Go system. If you are using very liquid materials (such as stains), it is better to remove most of the material from the brush bristles with a cloth or by turning the brush around briefly before placing the brush in the gel.