You don't have to. There are a few of us on here that skip the parasite cleansing. And you really don't have to after doing the Master-Cleanse because it also takes care of parasites.
You might want to read the Master-Cleanse FAQ's about when to Liver-Flush after the Master-Cleanse because some people do it a day or 2 later and others believe you should wait about a week. I've done it both ways and had similar results.