Tdog,
Cut the dang things down!! Take a look at the limbs hanging from the tree. If they are over your tank and field, there's a good chance that the roots have migrated to all of that yummy septic effluent.
We HAD (key word here) a Cottonwood tree that was 15-20 feet away from the septic field. Should have taken it out when we cleared the lot, but it looked "nice". After 11 years of filter clogging cotton and all of the small branches shed, it was time!! One of my neighbors came over and took it out.
Well, the "funny" part of this story is that quarts of water poured out of that tree right after it was cut. And, it kinda smelled. Hmmmm.... wonder why? /w3tcompact/icons/blush.gif/w3tcompact/icons/shocked.gif Needless to say, no more problems. /w3tcompact/icons/wink.gif/w3tcompact/icons/smile.gif
I guess what I'm trying to convey is get rid of the trees around the septic tank and field. As far as using some kind of chemical additivie, I can't comment on that. My take on using chemicals is to use them as the last resort.
Terry