When I put the baseball caps in the dishwasher, I unsnap the back, and resnap it around the bottom rungs of the dishwasher so they stay put. I put my dishwashing detergent in the cups as if I was washing dishes, and run it. A few times
, the colors on some caps have run. For instance, it might be a red logo on a blue cap, or some other insignia bleeding into the cap. I haven't had them transfer the color to another cap. Sometimes, if the sweatbands inside the caps or bills are extra dirty, I pretreat them with stain remover like Shout or Spray-n-Wash. They don't always come 100% clean, but they are always cleaner then when I started off! Do not dry in the dishwasher
: I take them out and put them on my clothes drying rack or over soda bottles on my enclosed back porch until they dry.
Note: Don't wash them with any dishes as the particles might adhere to the cloth of the cap and they would be dirtier than when you started off. When I have washed baseball caps, I fill up the dishwasher, both bottom and top racks with caps, and end up with about 15 or so caps at a time.