I always use Windex to clean up after acrylics (i use Gunze and Tamiya).
With my siphon fed brush, i'll either empty or spray out all the excess paint. I removes the cup and rinse all out in water.
Whilst the cup is removed, i then use an eye dropper filled with water and flush our the siphon of the brush. Then, i'll fill up the cup with water and spray out a few cups with high pressure, until is sprays clean.
I'll then refill with windex and spray a cup full through the brush high pressure.
Once it's all spraying clean, i'll take it all apart and use acrylic thinner on a cotton bud to get into all the smaller areas etc and all around the threads.