The rapid twist-turn oscillations in washing machines are likely to damage your brushes and machine inner drum too by banging them around. However, some brushes can be machine washed. It depends on what type of brush you’re washing and how you’re doing it. We just learned how to clean a horse grooming kit manually (using a bucket, warm water, and gloved hands). However, if you’ve got a heap of nylon-plastic brushes only, they’re most likely going to be safe being machine washed. Do not put your natural brushes in the machine at all. Keep them away from water.