trying to remove a 4 inch brass drain plug with a hex nut from a cast iron septic pipe. I soaked it with pb blaster and tapped on the plug, then put more oil on it. put a 24 inch pipe wrench with a 3 ft. cheater on it and it just rounded off the 2 contact points. house was built in 1952 and dount if it was ever off. the brass and cast look like new. any ideas for my next move? tia