It seems that having pigs downhill from a septic could be asking for trouble.
Though there are plenty of good suggestions here.
My concern would be that during a heavy rainstorm that there might be a possibility of an overflow. Though maybe someone has addressed this.
If you decide to do this I would like to offer some food for thought.
Dr. Bryant Redhawk has offered some suggestions for adding mushrooms to a system
here.
Best wishes for your success with pigs.