One method I have used with good success is get the kief through a 110 screen, place the kief in a 240 screen wad it so the kief is like a ball and shake on a cold day, what is left in the ball is not to bad...
R.C. Clarke describes this technique he saw in Afghanistan in his book "Hashish!". I've never tried this technique (which Clarke describes as lifting the fine mesh bag and dropping it down over and over again and this bag was passed around the room and that it takes a long time to really clean up the sift, he also said you could see clouds of fine dust (contaminant) passing through the fine bag.
how long does it take you to purify average tumbler sift into 80% + purity? Do you also use the lift and drop technique?