To check the vent. Watch the water level critically on one toilet while you flush the worse one. If the vent is obstructed or indaquate you should see the level change a little in the watched one. Takes two people.


I have never been faced with the problem you have. Yet if the vent Was pretty well blocked the load in the first toilet will be compressing air perhaps ahead of it. With a good vent I do not think the second toilet will show any or even the slightest change. Just a thought and test.


Your toilet is also acting a little like some plastic toy for example is stuck in the trap neck. Other than you have two other toilets with about the same issue. The toys seem to get contained and float around in the neck sometimes.


American standard stuff was really good at one time. Stupid company that ruined themselves with bad products.


Why it works sometimes and not others is also interesting. A toilet problem should in general be pretty consistant.


Bowl filling up with no action is pretty serious.