As others have said, the GWVR of your trailer is 3500 lbs. You are better off to think of this as the weight of the trailer.
It looks like the black tank is located near the rear bumper. Though it’s a fairly small tank (24 gallons), you will want to keep a fair amount of water in it. Not doing so could lead to a mountain of problems. The extra weight in the rear will lighten the tongue and in turn increase the potential for sway. My guess is that some sort of anti-sway hitch would be a good idea. I would not get one from the dealer. eBay, Craigslist, or etrailer.com would all be good places to look for a hitch.