I had a Winnebago that didn't have the valve attachments on the sinks like it is mentioned above. What they had were vents that went to the roof. I have had P traps siphoned by the motion of the liquid in my tanks because of a clogged roof vent.
This happened 10 years ago and I can still smell the stench
In my case, all I had to do is take a garden hose, climb up on the roof, take off the caps on my vents and push the turned on hose into each of the vent pipes. I had a vent that was clogged over my gray tank. I don't know what it was but all I saw was the water level rise in the pipe and then recede as the clog went was dissolved or pushed down into the tank.
That was the solution on that rig at that time. Have a look at how yours is built and see if this solution works for you.
As for suing Thor or the Dealer, forget about it. Not worth the time and money. You are better off playing the warranty game, make a list, give it to your dealer along with your rigg and they will take care of it. It will take time but it will eventually get resolved with people skills and patience. If you are out of warranty but have an expensive extended warranty, have your dealer work with it to get the repairs done. If all fails, don't sweat it, just fix it yourself with the help of your friends here in the forum. There are lots of people here that would help you.
Good luck with all that!
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