Step 1: Parts
a pair of buckets, check you local grocer's bakery, they'll often have them for free or a buck.
an air pump
a piece of pex tube 3/8ths
1/4 inch irrigation connector
barbed hose elbow
Step 2: The Bottom Bucket
drill a 3/4 inch hole near the bottom of the bucket, insert the grommet and barbed hose connector, attach the clear tubing. This serves both as a water level and as a drain, you can do with out, but draining will require disassembly.
Take the lid and drill several 3/4 inch holes in it, Snap onto the lower bucket and drill a 1/4 inch vent hole in the side of the bucket near the top.
Step 3: The Air Lift
Insert the air lift into the bottom bucket.
Step 4: The Top Bucket
Drill some holes in the bucket bottom, slide over the airlift and slip a piece of window screening into the bucket.