You may want to just ignore them, because some pipe plugs are not solid.
They look lke 1/8" pipe plugs, if you really want thm out, heat them up pretty hot and as they are cooling, apply paraffin to the outside. As the casting cools, it draws the paraffin in and makes it easier to get the plug out. Of course, then you have to have something else to fill in the hole!
R.