The bag is usually hung from the upper hull (tied and thrown over the hull) and has some sort of purchase system on it (3:1 or similar). You lower the rope putting the bag in the water, then you hoist the bag up a bit using the 3:1 (so if you have 100lbs of water in it, it's like pulling 33lbs on the rope). Then you use your righting line like normal but try to get the waterbag behind your shoulders - you push the bag outwards and it helps add to your weight. Seriously though, I bet you will be able to right the boat without the righting bag.

Say, are you going to bring that new ride to the Reggae Regatta at Lake Lanier in a couple of weeks!?