So, as you can tell, I'm a make up expert.. but I do know a thing about this make up clean thing.
What I do: rinse with warm water the brush entirely, but focus on the edges where the make up is touching the brush.
Then swirl it in a bowl of shampoo water (baby shampoo or something equally mild). I use a bowl like this with ribbed insides.
Then rinse it again until all the shampoo is out, and use a cloth to press and blot out as much moisture as possible. Then stick it in a place which gets a bit of wind (a small fan, outside, etc.) and it's usually done in a day or so. I usually forget them a few days in a row so ... I dunno the dry times.