A.S.
I never figured out a way to get them out. The only way I could prevent them was to stop using aluminum-based anti-perspirants. Yes, I sweated more at first (I'm a heavy sweater) but then to my great surprise my sweating dramatically decreased. I think my body was trying to expel the aluminum. It was so nasty.
I still sweat (not nearly as much though) but I don't get yellow stains.