Thanks very much for sharing.
I am sure the toilet's overflowing from the waste tank, as the intake line was shut off. Also the problem occurred with the valve in the "Dry" position. Our intake is only fresh water from the Stbd tank. I believe my problem occurred due to the waste tank being full, and as the boat rocks, the water sloshing in the waste tank resulted in pulsating pressure on the joker valve. Perhaps the new J valve with be less sensitive. If we overflow again, I plan to install the newer Jabsco toilet with the Twist’n’Lock handle, which is suppose to prevent flow back, or possibly an electric toilet.
Part of the problem was that , though we had just gone through a pump out, the tank was still filled. It turns out even with our vent line removed to prove we had a vented tank, the pump out station could not suck out much from the tank. So we'll try another station net time.
Any suggestions on how to determine that the W. Tank is near full? I don't find tapping on the tank to be accurate. For now we plan on being diligent about pumping out.
Thanks again for your thoughts.
Chris