Hi ! Welcome to IRV2! We're sure glad you joined us!
You should have a changeover valve where the freshwater inlet is located. That valve switches in the inlet from the freshwater tank to the inside plumbing. You connect the hose, set the valve to the tank, fill it to whatever level you want, then change it back to inside plumbing. I've never seen an RV without a valve like this.
Good luck, happy trails, and God bless!
Joe & Annette
Sometimes I sits and thinks, sometimes I just sits.....
2002 Monaco Windsor 40PBT, 2013 Honda CRV AWD