Understanding Sepp's Ponds

I've just finished reading Sepp Holzer's Permaculture and I thought it was fantastic.
I'm still having a hard time understanding how he seals ponds though. Could someone tell me in layman's terms, or point me to a video or something that could help me understand what he does to seal them? And what/why he uses the tubes as a drain?

Thanks!

There is a thread in here somewhere where he talks about this very thing.  He does it by agitating the bottom of the pond until the particles of dirt have settled out according to size.  If this forum's search feature works you should be able to find it.

Here's a podcast Paul made which has some info about the lakes he made in Tamera, Portugal...

http://www.richsoil.com/permaculture/166-podcast-016-maddy-harland-of-permaculture-magazine/

And here's the thread it inspired...

https://permies.com/bb/index.php?topic=7839.0

Someone I met on Reddit is going to one of Sepp's seminars in Tamera next month, and I'm rather hoping he's going to come up and visit for a few days so I can pick his brains.