Passin' Through wrote:
The purpose of the vacuum breaker is NOT to protect the RV water system, but to prevent a potential cross-connection with the campsite water system should supply pressure be lost. .... Please, for your own peace of mind and the health of other campers, make sure you have a functioning vacuum breaker on the black tank flush line.
This is correct. That vacuum breaker does fail from time to time. You do need a vacuum breaker in the line to prevent contaminating the water system. So you really should not replace it with a 90 degree elbow.
