I used to use a small air compressor from a big-box store. Actually still have it. Right after spending quite a bit of money on nice hoses and fittings to plumb the air into my newly constructed darkroom I was enlightened to the idea that blowing air off of negatives, film holders, etc. just pushes it up into the darkroom atmosphere where it inevitably settles on something else where it is not wanted and causes problems. So I adapted flexible plastic hose to my vacuum easel in hopes that the dust is now sucked out of the darkroom. The vacuum, by the way, is outside the darkroom. I fitted a small tube and brush intended for vacuuming computer equipment onto the darkroom end of the hose.