Black/Grey outlet valve replacement
Let me make you feel a little better about your experience. My wife and I purchased a 1997 Holiday Rambler travel trailer that had a slide out in the living room. It was a truely beautiful rig with tile floors in the bathroom, nice amenities, and all the whistles and bells.
I took it on our first vacation trip to the Great Smokey Mountains. I like to leave my tanks closed until they fill up and then dump them all at once. That keeps fumes from the campground sewer connection from coming up into the trailer. The travel trailer had a dump valve located under the slide out for the kitchen grey water tank. When I pulled on the handle to dump the tank the handle and shaft came off in my hand.
When I crawled under the trailer to check the valve, surprise, surprise there was no access door and the belly pan for the entire trailer was hiding the valve. So in order to get the valve open I had to remove all of the screws around the belly pan and drop it down. When I did nasty water came pouring out of the belly pan because someone at the factory ran out of sealing tape about half way around the pan and when we had driven through a major rain storm all of the water that sprayed up off the road had wound up in the insulation in the belly pan. It was full of dirt too. This meant that I had to pull all of the insulation out of the belly. Mind you, this rig is still under warranty, but I am a few hundred miles from my dealer.
I went to a local dealer and bought a new valve. When I took the other one apart all of the grey water from the kitchen, about 30 gallons, poured out on the ground around me too. I put the new valve in place and sealed up the belly pan. I figured when I got home I would fix the problem permanently.
I never got home first though. We stopped to spend the night on the road and the new valve did the same thing. I hauled the extra weight of the kitchen grey water tank all the way home. I contacted Holiday Rambler about the problem and what I could do to fix it and they informed me that they had never heard of such a thing happening and disavowed any responsibility toward the problem. Said I must have hit something to break the valve.
So I did a great repair. I cut the valve out of the pipe and spliced in a piece of pipe. I then bought a valve assembly that fit the 3" pipe coming out of the trailer at the dump location and glued it in place with some reinforcement braces. It didn't look as pretty as the original design but no more belly pan problems either. I reinsulated the belly pan, put sealant all the way around the trailer and reinstalled all of the screws using new stainless steel screws. No more problem.
This cost my dealer and Holiday Rambler absolutely nothing. I came to the same conclusion you did. Warranties are almost absolutely worthless. Usually when you have a break down you are so far away from a dealer you almost always have to fix it yourself. Then when you do get in touch with a dealer they will tell you that it isn't the manufacturer of the rv's problem, it is Norcold, or Coleman, or Dometic, or etc. etc. etc. If I took my Chevy to a dealer and he told me it wasn't Chevy's problem it was Delco's, or Delphi"s or Hydra-matic's problem I would hit the ceiling. I don't know why RV dealers can get away with this excuse. If Holiday Rambler, Fleetwood or any other manufacturer built it, it is their responsibility to fix it. Not the manufacturer of the component.
To bad they don't have a little foreign competition to wake them up like the auto industry did.