I you do not have a seive to filter out your small seeds (I do this with tobacco and petunia seeds), this method may be used. First make a tray out of regular paper by folding up the corners and taping them so that the seeds can't roll out. The take another sheet of 8x11" paper or longer and make a half cylinder and tape it to keep it that way. Do not crease the paper, keep it curved. Then position one end of the half cylinder in the paper tray at a low angle (to steep and debris will also slide down into the tray), but steep enough for seeds to roll down. Next, gently pour a small portion the unfiltered seed mixture at the top end of the tube and rock the cylinder from side to side. The little seeds will roll on down into the tray and the flat debris will remain at the top or slightly down from the top. Before you pour the next batch of seeds, remove the cylinder and blow away what debris was left to start clean again. It's slow, but if you do not have anything else, it's simple and cheap. I don't know if this would work with small seeds that don't roll so well.