ActionScript 3.0 :: XML Gallery - Properly Load / Unload Container MC

I have begun to build a vertical gallery. I have it set up to follow an xml document and it loads rather quickly. While the loading works, the unloading is not so hot. I can't figure out how to unload the container_mc which contains all the thumbnails. I intend to develop this page in as3 primarily so that I can adopt it to other projects. The arrangement is two vertical boxes on the right and left, a text box at the bottom in between the two vert boxes, and a fullscreen box in the center. The drawn squares are only being used as placeholders for real art right now.

As it stands, I can use either button to load the gallery, but when I click the next gallery it unloads everything, but it does not reload the next gallery. I want the buttons to load their respective galleries. I figure once I set up the structure for 2 galleries, I can make more.
var Gal_Array1:Array = new Array();
Was my attempt at loading the thumbs into an array, and later clearing it but I don't think it works (I think it would only double the amount of thumbs?). How to properly load and unload the container_mc?

Code:
import flash.net.URLLoader;
import flash.net.URLRequest;
import flash.events.Event;
import flash.display.MovieClip;
import flash.display.Loader;
import flash.events.MouseEvent;
import fl.controls.ProgressBar;
[Code] .....