Congratulations and welcome.
What model Gemini do you have?
Typically the fresh water drain will be right next to the tank, near the pump (all 3 will be in a similar location). Many times they will be behind a removable panel (look for a panel with a couple of screws in it--that usually means that panel is meant to be removed; otherwise it would be stapled in place). This could also mean under mattresses (if you have the floorplan with the two rear beds lift the mattress up on the passenger side bed and look for screws to remove). Perhaps a cold air return vent is screwed on? remove it and look behind it. Don't be afraid to do a little disassembly (just remember to put all the parts back in place
You can also look on the outside where the water fill is--the water tank should be near the fill on the inside; look in that area for a removable panel (or a drawer to pull out/remove).