The water level in my powder room toilet is very low. When flushed, it fills up but then lowers again. Plumber replaced the flapper and snaked the toilet but the issue persists. I see no water leaking from the toilet anywhere. When the toilet is flushed, air bubbles up also. Any ideas what the issue is?
I should also mention I am on the 12th floor of a 15 floor condo building.