If you're talking about the large 1" NPT plugs in the end of the heads use the following procedure to avoid breaking the plug or the head. Drill a series of about 1/4" diameter holes across the center of the stock plug as close together as possible. Take a chisel and break the material between the holes away. These stock plugs are cast iron like the heads so the material breaks pretty easy (same reason you can't usually unscrew them). Once you've broken the plug into 2 pcs, simply tap it out counterclockwise. Clean the threads if necessary with a 1" NPT tap. Usually not necessary if you're careful removing the plug. I've removed dozens of these successfully in this manner and it really doesn't take that long. Hope this helps