Gray Water Tank won't drain

[Jerapais69]

Well, a bran new Fuzion 427 and the gray tank won't drain. It drained last week no problem. It has 2 gray and 2 black tanks due to the 1/2 bath i'm sure. Guess i need to use that to clean dishes and shower!
ANyway, any ideas? I reverse flushed with a garden hose through exterior drain, snaked it, to no avail. I suppose i could go to roof and flush with hose from top as well but not sure of the 4 vents, which is which. Oh boy.......beat goes on...