Actually, chloramine can NOT be removed by boiling (only chlorine). Campden tablets work for both, though. I just measure out my total water for my recipe in my keggle (which has a graduated sight tube), and add the campden tablet then. Crush it up really well first, and stir well to mix in. It works almost instantly.
The idea here is that you want to remove it from ALL your water before you begin the brewing process. You don't want the chlorine to chlorinate any of the products of your mash, because they will wind up in your fermenting beer, which puts you at risk of developing chlorophenols in your finished beer.