I know, it sounds odd. But I've noticed that the water level drops about half an inch in the bowl of my main level toilet on windy days. I can see the water moving back and forth slightly, though there is no airflow over it. The level in the tank stays normal. The upstairs toilet doesn't have this issue. I am on a well, and the old septic tank was replaced a year ago with a septic holding tank that gets pumped to a remote treatment facility in the village. I don't see how this would make a difference, though. Any ideas why the water level drops in the bowl? Thanks!