2018 Montana - Are my tanks emptying?

[Mosnowman]

I recently traded my Cougar Fiver in on a new Montana 3721RL. When flushing my black and gray tanks on the Cougar it was obvious by the noise they were flushing. When I pulled my Black Tank handle for the first time on the new Montana I hear nothing? Gray Tank..same thing?

Here’s the strange part...

When I checked inside prior to flushing the black and the gray tank both registered 1/3 full. I did leave the black tank handle open when I went back inside and ran some water into the toilet. I went back outside and still nothing. The DW then yelled that the black and gray tanks were now reading zero fill. ?
I never did hear anything going through hose, and the hose didn’t have any residual liquid that I could tell left in it.

Only other thing I should mention is that this was the first camping weekend with the new rig and the temperatures dropped to a low of around 25 degrees overnight. Could this be part of the problem? Thoughts?