Air Bubble Causing Weak Flush Action?

[LarryLeveen]

A toilet in the house we rent has a weak flush. I looked at many of the usual things and cleaned the siphon and bowl jets. I observed the flush action with the lid off and saw a large air bubble by the tank seal opposing the downward movement of the tank water into the bowl. Have folks encountered this before?

I thought to check the tank-mounting nuts and was able to tighten one by hand. I will see if that help at all (and I'd be surprised if it did because no water leaks out of the tank) but I welcome other thoughts.

Thanks in advance.

 

[Jadnashua]

You can get a bubble back into the toilet if there's a partial clog down the line. The trapped air in the line may not be going up the vent, which could also be clogged. I'm sure that there are other possibilities.