This sounds like a problem that is basically just a fight with food, when in reality it is a battle with the self and self esteem inside of a person. You or the person suffering must deal with the issues that are triggering you to eat and purge for comfort, and you must be willing to put up a fight. When you or someone you know is ready to come forward for help, usually group therapy is the first place to go. Because so many people with bulimia feel incredibly guilty and ashamed, it is usually a helpful experience to talk with others that also suffer, just to know that you or the other person is not alone and has nothing to feel bad about. Overeaters Anonymos tends to show promising results for compulsive overeaters and people with bulimia, but if you are not a Christian you might have trouble following some parts of the 12 step program.
Individual therapy is key to fully recovering.
It is tough to deal with the issues that someone with bulimia has locked away inside all these years, but they must be dealt with so that you or the person does not have to constantly go back to purging as a way to comfort and bring relief to internal pain. As with anorexia, usually family therapy is suggested for those patients that are under 16 or 18 and have bulimia. I should make a note here, that those suffering from bulimia tend to have problems with substance abuse moreso than people with anorexia. You can not treat one problem and not treat the other.