How can the slaughtering tools used by a Christian butcher for slaughtering halal meat be purified if he also uses the same tools for slaughtering pigs, considering that he might use modern electric cutting tools?

To purify something that has been stained by pig's blood, it should be washed until the traces of blood are removed. This is sufficient with water or detergents, without the requirement of washing it seven times with earth. As for purifying knives and polished tools that do not absorb impurity, wiping them with a cloth or washing them with water until the trace of blood is removed is sufficient. If that is not possible, the impurity of the knife does not affect the permissibility of the slaughtered animal, and the parts that were stained by blood should be washed to purify them.