Flushing a toilet on SBB CFF FFS intercity trains: a guide for the perplexed

TIL how to do it. Basically, press the "WC" (dark letters on white background) on the wall to the right of the toilet; see image at right.

This was a puzzle on IC5, running between Zürich and Genève. If you know German, the "spülen" (which you can't quite make out on the image) might have been obvious, but I did not know that word until just now.