Pumping a septic tank is a lot like changing the oil in your car, its preventative maintenance. Waiting a long interval between pumping is like driving that car and never changing the oil. You can get people claim they've never had to pump their tank, and likewise people that go too long in changing their oil, but eventually there is a price to be paid for not doing preventative maintenance!

As far as bacterial additives go, the human waste and the tank environment will populate bacteria on its own. Adding yeast or bacteria (in the old days - dead chickens!) probably wont hurt a thing (other than your wallet), but it likely isn't going to be a noticeable benefit either.

Bill sounds like he has a grinder pump. That grinder is turning solid and liquid waste into a slurry that's going to have a hard time settling back out. Your filter plugging might be a result of this.