While the Franzinator sits between the compressor and the storage tank, the Air Polisher sits, according to Franzinator developer/promoter Franz©, between the air line and the tool you are using.
According to him, "The Polisher is really a cheap and dirty copy of a piece of equipment used in the refinery business coupled with a device used in the natural gas delivery business."
Here is a crude diagram of the Air Polisher. Examine the diagram for this simple device.
The assembly instructions:
Remove the valve from an EMPTY 20# propane tank, screw in a pair of 3/4" tees, and a piece of ½" copper tube.
The tube can be brazed into a bored-out plug, or if you can't braze, get a 3/4" MPT to ½" copper compression fitting, and bore the shoulder out so you can slide the tube clear through.
You'll need a drain fitting for the bottom "tee" so you can drain the accumulated moisture from the tank.
You'll also need a suitable fitting for the copper pipe to allow attachment of an air hose to feed your air tool.
Mount the assembled tank in the bottom up attitude, connect the air supply and your air tool as shown in the diagram.
Not having actually assembled an Air Polisher myself, those are the best instructions I can provide. At some point, I will construct a Franzinator and an Air Polisher and provide a more detailed materials list and some pictures. Until that occurs, more detailed instructions can be found here.