Trees and septic tanks question

Hi everyone, I am hoping there is someone who might know the answer to this question:

How far away from a septic tank should I plant a tree? I realize different trees might have different root habits, so there could be a complicated answer to this question. I want to plant a Nyssa Chinensis so that I can see it from the dining room window, but the septic tank is out in the yard on that side of the house. I could put it as much as 20 feet from the tank and still have it in view, but a little closer would be nice if not unwise. Or is 20 feet still not enough distance, and I should make a different plant choice?

Any help with this dilemma is appreciated.