I have been looking for a fellow toy hauler owner for quite a while now. Congratulations on your purchase.
I own a 08 mk-33 toy hauler ( crossfire ), and will help any way I can.
My coach has two water ports on the door side, they are the fresh water tank's fill ports.
On the driver side, the spray port is to spray fresh water into the black water tank, to keep the solids & paper from building up in the tank.--hook a water hose to it before you pull the valve open to drain the tank, and keep spraying until the waste runs clear.
The city water is just that,--hook the white water hose to it and thats it--you have city water & pressure to your coach.
The port just under the city water is the big mystery, I think it is to help with winterizing but, I am not sure. Anybody that know's for sure feel free to solve this mystery for me.
I am learning as I go, feel free to ask anything and I will be happy to help if I can.
Steven & Darlene Rees (Jacob & Nicholas)
2011 Chevy Siverado 2500w/Duramax Diesel
2013 Elevation 3612