How do urinals flush? (in the UK)

To most people urinals are a bit of a mystery. They seem to have a mind of their own and flush themselves almost at random (making them difficult to film). Have you ever wondered how they work? Probably not, but to fill a huge gap in YouTube I've tried to put together a few animations to explain the basics for anyone curious, including examples of how the most commonly used water saving devices work. Better just say I'm not a professional plumber so please let me know in the comments if you think I've got something wrong. Hopefully back out filming loos soon.