I have been an iv drug
user of pain pills for about 10 years now. I always use the micron wheel filters to filter out any bad stuff in the solution.
They work much better than just plain old cotton.
They cost around 3.50 each online each, but you can reuse the PVDF nylon membrane filters as long as you clean them with alcolhol after each use and then let completely dry, this way mold or bacteria can not form.
Or if you can afford it buy a box of 50 at a discount and use a new one everytime. Make sure o use the .2 size filters , they filter out a lot more than the.4 size since the pore size is half the size.
If you have to use cotton, msake suure to prewet them, and roll very tightly with clean hands. You may want to repeat the step at least 2 times to make sure you get out any impurities like celulouse or talc.