Dieselsmoke - how often you should pump is really a function of how large the tank is and how many people reside in the house. Like Roy, I do mine every other year, but I know some who do every third year. I think every other is safer. If the tank fills with solids (there is some natural breakdown that occurs through bacteria), one of two things will likely happen. One is the solids will exit the tank and go to the leach bed, which will in turn coat the leach bed making it impermeable, causing it to fail and forcing the liquid to the surface. The other is if the solid fills the tank, and can't exit to the field, guess where it ends up - back in your house. I used to adjust insurance claims, I've seen it happen, you don't want to live through this option.
I noticed you are from Eastern NC. My father used to have a property on the Outer Banks and he always thought it was odd that folks seemed much less concerned about the septic systems than we do in the Northeast. At least that was his casual perception, he could have been wrong. I don't know why, maybe there is some design difference. He just thought it was strange. Good luck, and I'd suggest you contact a pumping company or a septic system designer/installer to get their opinion. They will know a lot more than I do.