Where does it go?

[Onawayman]

I am in the process of making the furnace work in my 1986 sovereign and have a question. I see the ducts running to the front and back of the camper but there is also a small duct that runs through the floor and seems to turn toward the door. I know that is does not go to the bathroom because I can follow that duct to the plenum. Any ideas where this small duct goes?

[Alumaholic]

It's the holding tank duct.
It dumps heat into the space between floor and holding tank pan.

[Onawayman]

Make sense to me, thanks. Any chance of critters entering from here?