The answer is: I don't know.
But what I do know is that IF I write about it in an interesting way, then people will read about it, but the BEST part is when I get valuable input as a result.
"Why do you have to tell the world?"
I don't, but the thing is, I don't know what my network knows.
By putting information out there, the people who do know will tell me what I need to know. And this happens...A LOT. Which is why I keep doing it.
So, for the rest of you, here is Steve's note:
We had a similar problem. You need to put copper sulfate crystals in the system every 6 months or so. The crystals inhibit the growth of roots. You can buy it at Home Depot or online, and you just flush a jar of the stuff down the basement toilet twice a year. There also are some other stronger products that can kill off small roots before they grow. We had a similar blockage years ago and the plumber recommended this treatment. So far, so good.