Toto Aquia II flush problems

[Sarah Plummer]

Hi,
I've had 3 Toto aquia II for 10 years now, no real problems with them at all. They flush great, I don't even own a plunger.
Until a couple months ago. One toilet makes a large burble and bubbles at the very end of the flush. It flushes solids just fine, but it seems like there is a pocket of air coming back up?
Flush mechanism seems fine, comparing to other toilets there is not an obvious difference.
Only difference is that the water level in the bowl seems to be about 1cm lower than the others. Level in tank is normal (water line is consistent). If you flush toilet with nothing added it is normal, no burble, but if there is pee or solids to raise the water level to normal it burbles. I've poured water in the bowl and it will raise the level to normal but doesn't go past that.
I am thinking there's something up with the vent, I'm not 100% certain but I think this toilet would be on a different vent than the other bathrooms.
Any ideas?

 

[Reach4]

1. Do you have any AAVs?
2. Are you on septic?

 

[Sponsor]

 

[Sarah Plummer]

1. Do you have any AAVs?
2. Are you on septic?

There is no AAV under the sink, could be one in the wall?

No septic, municipal sewer.

 

[Terry]

Sometimes something like dental floss can wick water out of the bowl.
Normally water in the bowl helps with the flush. Sometimes there is something that didn't quite clear in the bowl, could be many things. The other day I pulled out a sponge from a customers bowl.