http://www.extension.umn.edu/distribution/horticulture/DG6986.html

That is a great link which states that 20' away from the beginning of the septic mound is considered the minimum distance for tree plantings. How about large shrubs that give you similar effects you want of Crab Apples and Cherry:

Service Berry
Grancy Greybeard
Viburnums

Those might work well for you!

Cherries and Crabapples tend to run shallow roots. The tree to avoid at all costs, is a Maple. Maples have a way of finding sewer lines and their roots can penetrate even concrete pipes. At ten feet away, you should be safe with medium sized ornamentals. Just remember, you will eventually need to have the tank pumped at some time, so leave room for access to the tank lid or access pipe(whichever you have).

Azaleas are also very shallow rooted.