Examples are the Upper and Lower peninsulas of the U.S. state of Michigan, the Scandinavian Peninsula and the Niagara peninsula.[1][2][3][4] The surrounding water is usually understood to be continuous, though not necessarily named as a single body of water.
A vacuum breaker is an attachment commonly placed on a bibcock valve or toilet or urinal flush valve, that prevents water from being siphoned backward into the public drinking water system. This prevents contamination should the public drinking water system's pressure drop. vacuum breaker typically contains a plastic disc that is pressed forward by water supply pressure, and covers small vent holes.
Also be sure a hole has not been punched in the bellows as this will cause a vacuum leak. The second thing that causes breaker to blow is simply an old worn out electric pump motor, especially in salt water applications. The third cause is that the holding tank is full and the vent line is plugged.