Ours (two of us) has been used for 24 years - never pumped and never a problem. I ran a gray water system so the laundry water does not go to the septic tank and we use liquid soap in the dishwasher. Little or no food residue goes in. Every now and then my wife throws in old yeast, spoiled dairy products, etc. to liven the bacterial array but we use no Rid-X or such.
Once in a while we will have a few - or as many as 23 - visitors for a week or more and they seem to be careful (after the "talk") about allowing nothing but human waste and TP go down the toilets. More than one septic "expert" has told us that the occasional infusion of loads of varied human waste from visitors is beneficial to the breakdown process.
Having helped a couple of other folks diagnose/deal with problems, I've learned that a long/strong pole with a slight paddle effect on the end can be helpful in determining the degree of solids in the tank. If that probe swishes around down there at the bottom with little or no resistance, you are probably in good shape. Rubber gloves recommended.
