Recently I noticed the toilet bowl wasn't filling up all the way after flushing it. When the toilet is flushed the water level goes up a bit higher than I thought it used to, then when the last of the water drains out it gurgles. When it refills, the level is about 3" below where it usually has been. It seems it is only being filled by a steam at the back of the bowl, but I've been told that not all toilets have fill holes all through the bowl that could get plugged. I don't remember if water used to run in on the sides of the bowl or not. We visually checked the tank and components and all looked to be functioning correctly. We've used plungers and a toilet auger, but neither has helped.

Remove the tank lid. Confirm that the water level in the tank is about 1" below the top of the overflow pipe. If not, adjust the float. Confirm that the little tube from the fill valve or ball cock is pointed into the overflow pipe.

You can confirm the maximum water level of the bowl by pouring about a gallon of water directly in the bowl. Pour slowly. If you pour too fast you will cause the toilet to flush.

Thanks for responding. I did check the water level and overflow tube and pipe, and all is good. Will checking the max water level just let me know if it seems to be filling too high immediately after flushing?

Do you hear and gurgles when you flush or drain a fixture. If the little tube from the ballcock to the white overflow tub and the level's OK the this could be a blocked vent. Let me explain. You flush and the water siphons out of the bowl. This causes a suction that's normally relieved by the lavatory vent. However, if the vent's blocked then suction could pull the bowl level down. The only other thing is if something were dropped in the bowl causing a crack that that lowers the level by seeping out the crack/
But it doesn't sound like that's the problem. If it were 5the bowl would fill up and gradually seep away. Cheers, Tom