One of those is this video tutorial byClean That Upon YouTube.
Get a large tub, then fill it with warm water, and add some dish soap or Tide.
After a couple of minutes, gently scrub the stain, then rinse, and let dry.
Image credit: Clean That Up via YouTube
This method can help your hat keep its shape and allow it to dry faster.
*All these images are credited toClean That Upvia YouTube.