Before my tx when i still had Colistine I would put the saline in with the powder very gently, didn't push the syringe hard at all. Then i wouldn't shake it but somwhat swirl it, gently but not that gently. Just enough that it would mix well but that it wouldn't foam.
It worked well. Or when it would foam i would leave it for 15 minutes (but no longer) before i would neb it.
I used used a <a target=_blank class=ftalternatingbarlinklarge href="http://www.romedic.nl/ventstream.htm">Ventstream</a> as neb cup