Making a pot from pipe doesn't work as well as it might sound. I have a pot that I had made from 12" diameter steel pipe. It is about 12" deep and dipping out to make ingots still leaves approx 1.5" to 2" of lead in the bottom. That will not come out. Just has to stay there until next time. If I had it to do over I would use an old propane tank.
Put that big chunk in a large pan and melt it with a torch.