I have two H&S Infinity AB's. After use, I always take the needle out from the back. First, I unscrew the rear part of the brush. Then I unscrew the needle chuck. After that I gently pull out the needle and clean it with an appropriate cleaner. Then I remove the nozzle and cap and clean those.
Next, I run 90% rubbing alcohol through everything and use a cue-tip to gently clean out all of the insides. Once I feel that all parts have had any paint residue cleaned up, I do the following:
Reinstall the nozzle and cap.
From the rear of the brush, I reinsert the needle, pushing it forward gently until I feel it seat in the nozzle.
Next I put the needle chuck back on.
Then, I reattach the rear part of the AB.
I've had trouble free use of my H&S brushes. I think they are great.