On my BayStar Sport the duckbill drain is on driver side just aft of the rear tires. On some models mine included, the overflow pipe will siphon out water from the fresh water tank as Newmar did not plumb it correctly. One or more threads on this. Some people have solved this my putting a clamp on the duckbill to prevent the water escaping. They will remove the clamp when filling the tank then clamp if off again for travel.
I have not done this “fix” mainly cause we don’t dry camp and less than a full tank upon arrival is ok by me.
2016 Newmar Bay Star Sport 3004
2015 Jeep Wrangler 2DR 4WD Sahara, Automatic, Hard Top