I found the leak.
The vent tube attaches to the side of the black tank near the top. This is where the water is dripping from.
I can see a hose clamp. Perhaps all that needs to happen is to tighten the clamp. But, I will leave it for the dealer to decide what to do about it.
Thanks for the help and support. In the beginning I thought I might be overly picky, because it only leaks when filled past top of tank. But there is still the situation of gas leaks.
It goes in to the dealer next week to add the swivel seats, so they can fix this at the same time, I hope.
It still has only 27 gallons of capacity instead of the documented 30, and that includes going halfway up the pipe towards the toilet. There may be an air bubble, but a 3 gallon air bubble is pretty big. The toilet bowl capacity is 2 gallons, so it is bigger than that.
Wayne in Coarsegold near Yosemite
2013 Forest River Solera 24R
2014 Jeep Wrangler Rubicon
ATV trailer for the following toys
2008 Yamaha WR250R,2009 Honda CRF150F
2008 Polaris Scrambler 500