"Packing" is what you put around a system with fluid to absorb any small, occasional leaks (say, from a joint flexing slightly under a pressure change), usually things like steam lines. This was one of the original uses for Asbestos, BTW. If you have a leak big enough to make it through the packing, well, it's messy to fix, but you have to because it generally signals bigger problems, starting with a serious loss in efficiency.