On the plug, I'd say the best bet is to puncture it in the center, then pry sideways to pop it out. This is the same way I do freeze plugs, just with different tools. A small flat screwdriver should do to poke a hole, or even just a nail and use it to pry also. With a screwdriver, use one corner of the blade so it punctures instead of driving it deeper.
If you get it turned sideways and it's not coming out easily, you can crush it with pliers or needle nosed pliers and it will fall out.
You may not even have to puncture it, just hit one edge and see if it turns sideways. Hit it down in the cupped part but at the side, not the very lip of the plug.