Toilet water level fills to normal water level lowers 20 minutes later. Tank water level remains normal.

[idreos]

When tank is flushed the commode level fills to its normal level but 20 minutes later commode water level drops about 2"
The tank water remains level so it appears the commode is slowly leaking into the floor flange drain hole
What is the likely cause of this?
Thanks for your help!

 

[Breplum]

1. Flapper

 

[Sponsor]

 

[Robert Gift]

Are there winds over the rooftop vent causing a slight vacuum pulling some of the bowl water out?
Likely more of an oscillation causing the water to go higher in the bowl and then lower and some of the water spills over
the trapway "hump" which determines the water level in the bowl.

 

[WorthFlorida]

Not possible that there is a leak unless the bowl has cracked. Robert Gift is most likely correct. My home second floor toilet does loses a little water. That bathroom is vented by an AAV. When a toilet is flushed down stairs or heavy use of water there is a slight vacuum created enough that the air pressure in the room is higher than the drain pipe and pushed the water down. I may lose a few ounces over a course of a day then it stops since the bowl water cannot go over the trap way.

 

[Jeff H Young]

bad bowl or wind likely causes flapper is unrelated to the bowl

 

[GReynolds929]

I've seen where toilet paper can get stuck on the trap outlet hang over and wick water out of the bowl.