Filters.

[TheUltimateFixx]

I'm not a fan of common cotton wool because it so easily comes apart in fibres that will clog needles and when they don't do THAT, clog your blood vessels instead. Cigarette filters contain ground glass which makes me a little bit skeptical of them ; also they filter out less than half of all particles in the 10 micron range, and drug retention is on average at 0,13 ml (compared to a syringe filter which will seperate out up to 99% of insolubles while retaining only a minimal amount of your drug, 0,02 ml average).

So syringe filters are definitely the ideal,
(and the only ones I'll use for myself these days because I no longer have to contend with physical dependency) but their one drawback is if you're in a hurry, or shaking from withdrawal, they can be a bit difficult to use. You need to fit them on the needle and you may not have the patience or co-ordination at any one given time to do so.

So the best intermediate option I found is dental cotton. (Like what your dentist shoves in your mouth to dry it out for a procedure.)

It has better filtration than your common cotton because it is denser, and for that reason also doesn't shed so many fibres that can end up where you don't want them. Easily ordered in bulk via websites like ebay and Amazon too. Just thought I'd put this out there.