Spitfire 1500 wrote:
Situation:

I flush the upstairs toilet. It flushes just fine.

About 3 minutes later, the other toilet downstairs does the end-part
of a flush. I can hear the valve downtsairs close(makes a reassuring
"thunk" sound).

Did a little experiment. Flushed upstairs toilet, ran downstairs and
watched the other toilet. The water level in the tank goes down a
bit, and it of course flushes back to normal level.

Any remedy for this?

Clear the obstruction in the vent pipe. Other possibility that I can
think of would be some kind of problem with the flush valve.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math