I take the bungs out with a bung wrench and, using a garden hose, run several gallons of water into the drum. Them, I use a 4 1/2 inch cutting wheel too start an opening. Lay that aside and using a metal cutting blade on a Sawzall, I put the blade into the beginning slice, and run the Sawzall around the drum with the guide /guard against the edge of the drum. After I finish the cut, I set the cut out section aside for use with jacks, etc. I take the cutting wheel and cut the area out to the rim of the drum in multiple places like the minute marks on a clock face and bang them down with a ball peen or small sledge hammer.