There could be something to the EnviroTube issue. I had one installed 3 years ago. No problems but a contractor said that there was some issue with the company designing and selling the tubes and what they were really designed to handle (bumped into him this year). Further details are hearsay so I will stop there. Point is, I will be getting mine pumped every year as opposed to every two, at least while my kids are at home.
Edit: Going to add a few things. The grit size for the sand in these fields are important. Had a septic designer tell me that. It is a very specific grit. The other thing is, we all use our fields differently. I am a miser.. no cooking fat, no flushable wipes and i throw my snot rags in the waste bucket. Some families, especially if they move from cities with sewer systems, into a home with a septic system, can be brutal on the system.