I went to my local HVAC guy and had him make me a washable filter for
$10. Some sort of rubber covered hair like stuff. I also got a spray
bottle of soluable oil to help pick up the dust. Every month I simply
give it a hose down in the shower, let drip dry, and spray again. This
is what I did many moons ago with the filter in an old Tektronic
oscilloscope.

The friction loss in the pipe/ducts is the main culprit. I have had an
electrostatic air filter and mechanical filter backup in one house I
owned. Had to turn a hose on it every 3-4 months, and also used the
filter oil on the screen, which became FILTHY!