It is a filthy job. Unfortunately there's no way to really tell if the joint is re-usable until it's cleaned. If the boot has been torn for long there's a good chance it has been contaminated and the races are shot like this one:
The easiest way I found to wash them out is in a coffee can with 3" of paint thinner or kerosene, then a dunk in warm water / Dawn dishsoap.
-C