We have a brand new two storey home. The water in all three toilets seems to disappear. We have noticed on windy days that the water moves back and forth in the bowl and the water seems to dissapear quicker. The vent appears to be free on all toilets. They even cut down some vent to see if it would help but hasn’t.They replaced one toilet thinking it may be the problem but never helped. Is this a syphoning problem? Any solutions that I can pass on to my builder?