This is a very complex topic and one that must be approached in many different ways. No 2 ways seem to be the same when it comes to removing the taint of evil magic it seems. Some are done through solemn rituals and with powerful magics aimed to draw out the evil while others have been done by using the cursed or tainted weapon for good and just causes or through heroic sacrifices and still, others have been cleansed with things as simple as Remove Curse magic. Magic, like a living thing, has it's own unique qualities and vibrations and so, there is on 'one sure-fire way' to remove negative effects from something.