i used foam ear plugs rather than corks to fill the ends of a tube i was casting then put it in the pressure pot....yeah, that didnt work like i hoped. the pressure pushed the plugs into the tube and they soaked up the PR.
I'm a little surprised that the PR didn't eat them.
Were you able to remove them from the tube? You may have to drill a hole down the center of the tube and then knock out the mess. Depending on what you were casting, the blank may be salvageable with a repour.