Designing Kitchens and Bathrooms - Hooking up waste water drains to existing septic

I'm adding on a bathroom as part of a Master suite... The septic system I had installed 5 years ago was intended to take on this new bath. How do I connect the waste drain system to, I guess not the galleys, but the main... cylinder, is it? Do I break into the existing drain, or do I attempt to add a second, seperate access to the septic 'container'?

I will of course refer to my local building codes, but I'll take any input/advice out there, since I'm new to that phase of plumbing...

Cut into your main drain line with a sanitary T from the new bath toilet line, and connect smaller lines (sink, tub/shower) into that line. Be certain that you are venting all properly. Slope all drain pipes 1/4" per linear foot.
No need to run new line all the way to septic tank.
Check with your local building inspector for code, permit, inspection requirements.
Good Luck!