Well I just used my exterior antifreeze inlet a few days ago. If it is like my 2306 then it is only for winterizing. First drain your water like normal and then hook a regular male threaded hose fitting with a clear hose to the inlet.(Doesn't have to be clear, but I like to see the antifreeze in the line.) Then stick the clear hose down in a gallon jug of RV antifreeze. You should have a shut off valve to your fresh water tank so go ahead and close that. You only want to draw from the antifreeze and if the fresh water tank valve is open then you will probably suck air from it. Then if you want to bypass your water heater go ahead and do so. From there you just turn on your water pump and the antifreeze will be drawn into the water lines and you can winterize as normal. If your not sure of the winterizing process, there are a few videos on youtube demonstrating how to do it. The exterior antifreeze inlet is just a convenience so you don't have to swap out lines to the water pump inlet during winterizing.
2016 Ultra Lite 2905SS
2014 Chevy Silverado 2500HD