We have two toilets on the second floor of our house. One toilet has
frrequent but intermittent weak flush. A few flushes in a row might flush
strongly, then one, or maybe two,will be weak. The water in the toilet never
quite gets beyond a rapid swirl. And then there's another strong, complete
flush. Mind you, this is with nothing but water in the toilet. When I say
"in a row" I mean simply letting the toilet tank fill completely and then
flushing the toilet after each fill.

We've had a plumber use a snake to make sure nothing is lodged in the "S" of
the toilet. He said it could be a bird trapped in the vent that exits the
roof, and that if we bought a new super-dooper water-pressure toilet from
them ($900 installed) they'd run a snake up towards the rood and down
towards the sewer from opening in the bathroom, at no extra charge. He
lifted the tank lid to look inside, and noted that some bubbles were coming
up into the tank but did not explain the significance of this symptom. What
do bubbles coming up into the tank point to? Is the toilet not seated
properly on the lead pipe in the floor?

Thanks
Timo