Pipe organ pipes are usually TIN alloy not lead. At least the ones I have seen. I just missed an entire church organ worth of pipes once. I was most bummed.
As I understand the process sulfur bonds with the zinc contamination and allows pulling it out as dross, with the possible drawback of also pulling tin with it. There might be a sticky on it in this forum I think. So for WW batch that you accidentally melt a bunch of zinc ones in sulfur is supposed to be a way to drive zinc percentage down to where you can cast with it.