'New'........take it back to dealer and have them fix
But if this new is your 2011 Montana then you need to clean/lube toilet bowl seal and ball valve.
This means getting in there with your hands....old soft toothbrush and scrub seal top/bottom flexing seal as you clean it and the ball valve. Then rinse it clean and wipe dry. Using olive oil or plumbers grease (no vasoline) lube up seal thoroughly and ball valve.
If after cleaning/lubing and it still doesn't hold water........replace seal.
Water in toilet bowl provides a vapor barrier and is how toilet should work