What can (and cannot) be put down drains that are connected to septic systems?
Tooth paste and soap (even a little anti-bacterial) are certainly fine.  Basically, you just don't want to put any harsh chemicals in there that will kill the bacteria eating away at the waste.

I would avoid food and thicker items as they will not break down.  I try not to allow hair, coffee grounds as they might not break down.  I would definitely avoid paint.

Also avoid paper products that wont break down.  Feminine products can cause havoc.  Almost all toilet paper is septic safe these days, but read the packaging to be sure.

If you just bough a new house, or built one, I would recommend you have someone come out and pump the basin sooner that later.  That way you know for sure that the tank is clean and in good working order and you can have a fresh start.  I have heard way to many horror stories for new builds where the contractors used the tanks as a trash can and that later caused problems.  Then remember to have the system flushed out every 3-5 years based on usage and local laws.