The black tank valve could be as simple as it being left open during the PDI at the dealership and then not being able to close it due to the black water and solids in the pipe. If it is just that - and while that's likely it could also be something more significant - after the tank is empty it should be able to allow the gate valve to close.
Just to be clear, Im on my own with these issues. Neither Ford nor Winnebago have provided any help or support
It's a very hard lesson to learn for a first time new RV owner that you are pretty much always going to be alone with these issues.
So, I have a significant asset, parked and I can’t use it. The unit itself is nice, and things will probably work out. But, these events have really taken the joy out of RV ownership.
Don't let this get you down. It is EXTREMELY common for new RVs to present not only new learning challenges to you at every turn, but it's also all to common for new RVs to rack up some new fresh issue with every use for the first few months up to a year.
You'll learn that Winnebago is in northern Iowa and not really equipped to help out on most things. And, dealers are buried under way too many other service calls to "fit you in." And even when they do many times they are not much actual help.
You've bought a house that is built upon a truck chassis. It's not at all like buying a car. It's not designed like a car, built like a car, sold like a car, nor serviced at a dealership like a car. You'll be happier with the purchase when this reality sinks in fully.
Trust us here to help you and if we can't help directly we can likely point you in the right direction. Soon, you'll be an experienced PRO and handling problems like a boss.