Sometimes Thor doesn’t get all the crud out of the tank before assembly. On my other Thor they left the cutout in the tank when they drilled for the pipe. Try leaving the valve open and flushing with a lot of water, if that doesn’t work you’ll have to take the valve apart to get whatever is blocking the valve out. If you have to take the valve apart I would suggest an old towel under the valve to catch drips and a pair of rubber gloves.
Dave & Myra
One day your life will flash before your eyes,
make sure it's worth watching!