Hello, we just bought a 2014 Aspen trail 2760 bhs. The previous owner fever used the fresh water tank. We just took it out and in the way back we tried to empty the fresh water tank. I unscrewed what I thought was the drain but no water comes out. If I turn on my pump though, water comes out of the low point drain. I even took that while valve out of the pipe and still nothing. Am I missing something?