Can the Vacuum breaker-check valve be py-passed and replaced by an external vacuum breaker-check valve so that it does not leak inside my 2007 Saferi 19' Bambi every time I use the "No-Fuss Flush".
I assume you are talking about the blank tank flush. If so you either need to replace the valve or simply remove it. There are several posts about this issue on AF, and there are obviously pros/cons for each. If you want to replace it I believe there are higher quality brass valves available. I removed mine and replaced it with a PEX elbow.
Well, there is a valid code reason that it is there. I cannot recommend simple removal. A new one is not that costly. Just remember to blow it out with air when you winterize and you won't have to replace it again.