I do believe that this is the Desiccant plug (see pic below). This thing is really tight to the point that I feel that I might brake it trying to unthread it.
That's pretty unlikely - it's metal. You should be able to use fingers; if you can't get a good grip, a silicone jar opener or rubber band might help. Avoid vice-grips etc. It is threaded, and there is a neoprene-like o-ring to seal it, so it can be stiff. Are you having a problem with frost?
No problems with frost, But I haven't used the camera (other then bench testing) since last March. I thought that I would recharge it before I took it out to the Observatory. Is there a dummy plug to install while recharging? If so, I didn't ever see one in the camera case.
BTW if you haven't had any evidence of frost, you probably don't need to bother with it at this time.
I do recommend refreshing the plug once every two years in dry locations, and once every year in a high humidity location. You don't really want to see frost on the sensor. There is normally no need for a dummy plug. Just make sure you're in a reasonably clean and dry environment. Place the camera on a desk with the desiccant port facing downwards, just to protect it from any dust floating about.
