In my humble (and possibly incorrect) opinion, I believe that using a cotton ball, Q-Tip, micron filter, etc...is not needed nor useful for preparing a nasal solution of Subutex (and only Subutex, Suboxone is different and I imagine that filtering may be useful)
This ONLY applies to the "Subutex" pills as I just stated, while I don't have experience making nasal solutions with other pills I'm sure filtering those pills would confer some sort of benefit.
The reason I believe filtering Subutex would serve no purpose is b/c IME, the entire pill dissolves in one's mouth leaving zero non-dissolved / insoluble particles behind. Since it appears nothing in the pill won't dissolve in water, I don't see how filtering these pills could be of any use---theoretically, the entire solution should pass through the cotton, thus the cotton is useless.
Suboxone on the other hand is bright orange, so even filtering out some of the coloring would probably be a good idea.
DISCLAIMER: This is just my opinion, my theory. I could very well be wrong and please welcome others to correct me, also, to reiterate, my theory ONLY applies to the white, brand name, Subutex pills and does not apply to generics, Suboxone, or any other type of pill...
Just my thoughts....
Also, if some medium other than saline was used that was able to dissolve the Bupe but not dissolve some of the inactive ingredients that are otherwise soluble in water/saline, that would seem very helpful in not only allowing the inactive's to be filtered, but also in allowing the solution to be made at a higher concentration, therefore less liquid would need to be squirted into the nose, minimizing the amount that drips down the throat or back out of the nosril....Unfortunately I haven't the slightest clue as to what medium possesses this type of property