That's the diff and if memory serves, that'd be about where I'd expect the drain plug to be. I keep forgetting, but either diff or trans. gets a crush washer on that plug. For now, tighten it and see what you get...not crazy tight though...search for torque on it. Maybe 40-50 lbs., if I was guessing. Of course, if I'm right, you'll also sort of want to get it raised, level, and check the level from the fill plug, unless you know it's just started.
Usually, you remove fill plug first, so if you have issues with drain plug, you can still drive it...after returning fill plug, of course.
Realoem.com will tell you if you need crush washer there, coz if the tightening doesn't work, then try crush washer...which means a drain. If the level is fine, just tighten a little, keep your eye on it. There's only a qt. of fluid in the diff.