"C & M" wrote in message
...
Have someone go up on the roof and push a running garden hose down the
vents
stacks to push any obstruction and flush it at the same time. Did this
once
many years ago with good success.

e.g. bird's nest fell down vent stack pipe?

Also; we suspected slightly rocking toilet for recent smell in our bathroom,
although it is foam rubber not a wax seal. However smell was due build up
of brown grunge in the wash sink over flow. Don't know why, but it did.
Pushed a piece of that spirally/flexible curtain hanger wire up and down the
overflow slot in the sink to dislodge, flushed with hot water etc. few
teaspoons of 'Javex' etc.
Wasn't the toilet at all! Now properly chocked.