Definitely sounds like the drain is open. Not sure which unit you have, I have the XG32 and the fresh water tank is under the bed, lift the mattress and there is a door you can open, big ball valve in the drain to close it.
Thank you both so much for getting back to us. The Thor Owners manual that came with the coach are not very informative. We just picked her up on Friday and have been trying out all the systems. I'm sure we will have more questions