I recently ordered a few "brush eggs" to clean my makeup brushes with.
I keep one in my kit and one at my makeup station.
From the website
BrushEgg is used to help with the deep cleaning process of makeup brushes. The BrushEgg is, - Compact - Quick, Easy, AND Effective! - Reduces the use of Brush Cleaning Solution (which dries out bristles) - Use whichever Soap or Shampoo you choose - Smaller knobs on top used for Foaming & Lathering - Grooves on bottom used to agitate bristles just enough to release product, dirt, and oils without stripping them Smaller knobs are also ideal for smaller eye brushes (Fan, Liner, Smudge, Pencil) for extra gentle lathering and releasing of dried on products.