It is a common problem, and not just a Jayco problem. My first experience with it was on my JayFlight 25RKS, and discovered the same problem with my Heartland Sundance XLT. A short piece of wood dowel will fit right in my pex over flow tubes and plugs them off. Kinda red neck, but it works well and the price is right. Remove them when set up, and plug them back off right after filling the tank.
Becky, Bob and Taylie & Bode
2009 Silverado 2500HD Duramax/Allison
2014 Heartland Sundance XLT 245RL