My Itasca Class C is the 324V model (often just called the "24V" model).
On the passenger side outer coach wall way at the back is a large access door for the largest exterior storage cabinet. On this exterior coach wall and just a short distance from the upper left corner of this cabinet door is a small white lockable flip-door covering the gravity feed fill-opening to a pipe that leads 2-3 feet to the top of the fresh water tank, which is in the coach's interior underneath the rear corner bed.
On the driver's side exterior coach wall is also a hose fitting for connection of a hose to supply the interior fresh water system when on hookups. From this hose fitting I cannot fill the fresh water tank. I must use the gravity feed flip-door on the other side to gravity-feed fill the tank. This hose fitting on the driver's side exterior wall only leads to all of the interior fresh water plumbing and directly to the faucets, the shower, the toilet, and the exterior shower .... when on hookups.
Inside underneath the rear corner bed is stored a built-in (by Winnebago) long clear plastic hose coming from a swith-over valve for drawing from any container I want for pumping into the interior piping - such as anti-freeze for winterization. Instead, I could draw from a fresh water container to supply water to all of the interior water system plumbing - including the exterior shower.
It so happens that the exterior shower head is just inside that large rear storage cabinet that is right next to the flip-door opening to the pipe to the fresh water tank that I mentioned above. This means that I can turn on the water pump and draw from a fresh water container inside the coach with the system under the bed setup (accesible via an access door) intended for winterizing. While doing this, I can have the exterior shower hose routed for pumping into the fresh water gravity feed inlet opening I described above ... which is right next to the exterior shower hose and head which are just inside the large exterior storage cabinet.
I don't think the Winnebago designers planned for this special very convenient situation, but I could use this approach to fill the fresh water tank from a container inside the motorhome using the built-in winterization configuration, which would utilize the built-in 12V water system pump to do the pumping. There is even a water pump ON/OFF switch right in the larger exterior storage compartment for turning ON the water pump right there where the exterior shower hose is.
It's a sweet arrangement - probaly all by "accident". However, I've read other threads in this forum describing this same approach others have been able to use with their particular RV setups for filling of their fresh water tanks from portable containers using their built-in winterization systems.
P.S. It took so long to write the above that I probably could have went outside and took pictures for less writing and more clarity!