Roots infiltrate where there are nutrients. So septic systems and sewer lines are prime 'targets' for roots to get into. Not sure they'd be as much of a threat to a foundation unless they were attracted to the out-flow pipe to the septic system.
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."