I soak any brush I use(primarily a #6 horse(?) from bestshave), in my lather bowl filled with hot water, for the duration of my shower. I stand the brush up in a wash cloth in the bowl and so only soak the bristles not the knot.
I'm with Ryan on this one - no need to soak a badger. I just run it under warm water and start lathering!
A badger brush doesn't need extra soaking - unlike a boar brush, which takes a few minutes to absorb water. A few seconds in water will do the trick