And more important is no trees or shrubs anywhere near the sewer/septic/leach lines. Once the roots get in you can not get them out.
Good luck DE. I think for a permanent fix replacing the line is the best way to go. I'm curious how old the house is? That would tell me what kind of drain pipe it is. Clay/Cast iron/PVC, just can't see PVC/ABS cracking and letting a root in. You guys up there do get earthquakes and that could have cracked the pipe. Be really interested in this.
Good luck and let us know where the root got in and what kind of pipe you have.