Issue with water system - am I a bonehead??

Hi all - new (to me) 179. Going about process of dewinterizing. Added water to freshwater tank, drained it off to remove residual antifreeze; found that most of the water was ending up in the gray water tank. Same thing happened when I sanitized the tank - added chlorine to freshwater tank, and topped it off. When I went to empty the tank this morning, I found that the freshwater tank was empty and all of the water was in the graywater tank. Checked for the obvious - no faucets were open. Is there a valve somewhere that I do not know about? Or is there something else going on here?

No, its not that - I filled the tank (not the threaded city water inlet). I've had trailers before so am familiar with the basic operation. This one's a mystery to me. Looked under the bed to see if there are any valves I was not aware of. There's one coming out of the water pump outlet (open). Any other ideas, anyone?

Looks like I found the problem - leak somewhere in the toilet, water running into the shower drain then into the gray water tank. There were a pile of towels in the bathroom so didnt notice it. Now to figure out whats causing the leak....

Originally posted by Ben Herman Looks like I found the problem - leak somewhere in the toilet, water running into the shower drain then into the gray water tank. There were a pile of towels in the bathroom so didnt notice it. Now to figure out whats causing the leak....

My best remote guess is broken toilet flush valve.

Aha!, the mysterious pile of towels.  Hope you get the valve fixed without too much hassle.  Did it overflow the toilet?  If my wife caught me with that batch of towels, we'd be on our way to Costco to get some new ones and she wouldn't even let me wash the old ones in the washer to use as rags.  I'll bet your fresh water pump really got a good work out.