I just read this in my new FMCA Mag and thought I would pass this along since there was some discussion about P-traps not to long ago.
Looks like a nice alternative and space saver under the sink. There is basically a bladder in in that only allows water and fumes to go only one way. And can be installed vertical or horizontally. Pretty cool
Here is a link to Hepworth: http://www.hepworth.co.nz/HepVo-Intro.htm
There are benefits and FAQ to the left of the page.