Toimii kuin junan vessa.
- a contemporary Finnish proverb =)
This is a rather new expression that is used to say that the thing in question works flawlessly in every possible condition. Used to describe all sorts of mechanical and electronic devices.
The roots of the expression can be explained easily. The 2nd class cars on VR's trains on normal long passenger routes have very simple toilets - basically, just a toilet seat with a hinged metal bottom that can be opened with foot pedal (that also triggers the flushing). The hole on the bottom leads through the floor of the car, so the waste ends up on the tracks - there are some "Käymälää saa käyttää vain junan liikkuessa" ("the toilet may only be used when the train is moving") labels on the walls that get vandalized to the form "Käymälää kyttää junan kissa" ("the toilet is being watched over by the train crew's cat").
This sort of device cannot misoperate. It's just a hole. Gravity does most of the hard work. Even if the bottom gets stuck to the open position, the toilet still works as it's supposed to work (even when the user may have some discomfort during the winter, but less discomfort than what they get for waiting until the destination).
(Of course, VR's InterCity and Pendolino trains have much more complex toilets that reportedly don't work like train toilets. Thus, this expression is used less in the South =)