Like you mentioned, a GDA can help. I would say it helps more with controlling bloat after carb heavy meals than having to do with water retention. I have tried several amounts of carbs with 2 caps of SlinMax. The most I have tried in one sitting is just under 150 grams of carbs for that meal. Even after all that, I am still hungry, I have no bloat and I look tighter. It helps provide me with a pump as if I were jut lifting. The full dose of Na-r-ala and agmatine definitely help there.
I would look at two things also; sodium intake and water intake. I know it may sound counter productive, but you want to drink water to help lose water or two just keep your body from retaining it. If you're depriving your body of water, it will try to hold onto what's there. Also, having an adequate amount of salt helps too. Again, you do not want too much, but you still want some. You should not fear sodium. Sodium will also help with getting those veins out.