In the convenience center probably a little above the city water inlet there is a screen. That is the vent for the fresh tank. If I remember right, some members have used that port to add water. I don't camp without hook ups so I'm not that versed, hopefully someone will have the definitive answer.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.