To get a fecal sample, put the turtle in a pan of warm water and let it soak. They often defecate then.
In southern california, you should be able to let it live outdoors year round without problem. Make sure it has a big mulch pile to bury in for winter, and that drainage for it's pen won't let it be flooded out.
It is not unusual for them to remain still and inactive for days at a time. It's not the most fun to watch, but that's just how they are. If I don't see one of mine for a week, I find them and make sure they are doing okay.