We have essentially the same model, a 262RKS (2014) and that model will be a 261RKS, not 26RKS. We've also previously owned a 261RKS.
Check the frame carefully. It will have the type that is fabricated from 3 pieces of sheet steel welded together which looks like a regular forged I-beam. These frames are not as strong and flex a lot more. Look for cracks near the spring hangers (
see this for example. Make sure there is no uneven tire wear. Check the suspension carefully.
This particular model is tongue heavy, not light. I've weighed ours at a scale and the tongue wt. is just under 1,000 lbs with one battery (up from 540 lbs factory dry wt.) and just under 15% of the GVW. I also found that the total TT weight is about 200 lbs under the GVWR rating of 6800 lbs when fully loaded for camping. Towing with a full tank of fresh water may put you over the GVWR so if you buy it, I suggest going to a scale to find out what it really weighs.
I agree that the black tank is harder to empty and clean on these. I get ours totally clean after each dump but it takes more time and work. I fill the tank to full, then dump. Then I use the built-in tank rinser for 5+ minutes, then I fill the tank to full again and dump. I then repeat this process one more time and then it's usually spotless and if not, one more repetition will do it. With the water off, you can look down the toilet to the tank bottom to see if it's clean.
The rear kitchen is a great thing to have. The bathrooms are quite large which is also nice but unfortunately they made them smaller for 2014 by putting in a rather large shower stall.