My super & I are stumped. We have a unit that the water level decreases after about 2 hours to almost nothing. It makes no sounds; i.e. gurgling, bubbles. There is no water on the vinyl, or anywhere else. The unit has been occupied for sometime, and only recently developed this problem. The wax ring is good, ( I'm assuming, due to no water in unit or down stair. We're using the Fluid Master. The flapper is sealing. Got any help? Thanks in advance.