Deadeye, might look through these:

http://www.crappie.com/crappie/south...-get-bait.html

To keep from posting links to other fishing sites, go to Google Images, and copy/paste this into the search bar:

5 gallon bucket bio filter for bait tank

That will show you some pics, those that interest you will take you to the site they were posted on if you click on the pic. I saw some that would probably interest you. Wikipedia also might have some info on the biofilter as well. I've seen a few, 5 gallon bucket (biofilter) with holes in the bottom, hanging over the bait tank, water pumped out of the tank, into top of biofilter, filtered water drains out bottom of bucket back into tank.