I am trying to diagnose a sluggish toilet flush. I want to determine
whether it is the toilet, the stack drain or the vent.



I have four toilets in the house (three on the second floor), and this is
the only toilet that has a problem. This is one of the second-floor
toilets. It is an older 5-gallon toilet.



If I flush the toilet, I get a strong water flow into the bowl, a strong
swirl, and a strong whirlpool. But no siphoning. The water level in the
bowl remains high throughout the flush. When the flush valve closes, the
swirling stops, and the water remains at that level, instead of emptying the
bowl through siphon action.



If I keep pouring buckets of hot water into the bowl, one after the other,
two bucketsful siphon empty, but every third bucketful leaves water in the
bowl (at the normal, neutral level). The fourth bucketful drains empty
again.



Fishing with a toilet snake, I cannot find any blockage in the trapway. I
have not tried removing the toilet to fish from the bottom (that is a last
resort).



What are your thoughts?



- David