Aerator Plant Upflow Filter

I have a 1200 gallon wastewater aerator plant, with an attached gravel upflow filter. I have the tank pumped out every 3 or 4 years, and at the same time, have the gravel filter backwashed.
I would like to backwash the gravel upflow filter myself every six months, but I don't know how to do it. Surely it doesn't require pumping out the main tank! But just what does it involve? The aerator companies want you to have authorized service personnel do this job, so they don't tell you how to do it. All they say is that it is a simple procedure and should be done every six months.
I've googled this subject, but have come up empty. Also, I have searched the web site of the company (Jet, Inc) that manufactured the aerator plant.
Any help would be appreciated.
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