its a vacuum line so fluid would be sucked in regardless. as far as raising it above the tank when sitting... that would work but only until it was fired up. and running. That failure scenario would only happen if the o-ring and diaphragm failed at the same time. highly unlikely.
But would warrant a new, rebuilt or manual petcock IMHO.
m in SC, I can see that what you said about the dual failure is correct now that I'm rebuilding the petcock. I apologize for doubting and contradicting you.
On balance from all the advice everyone has posted, I don't think I'll bother with the solenoid. I can see what people are saying about crud being the underlying cause which would also eventually affect the solenoid valve, delaying the inevitable.
I can also see that the vacuum line is not the issue since there would need to be a failure of not only the oring but also two diaphragms (with a weep hole between them).
I've got an epoxy coated tank, new seal and diaphragm kit in my pet cock and a new fuel tank cap on its way so hopefully that will suffice to provide freedom from the hydrolock nightmare.
Thanks everyone.