There is a buzz on a new plumbing part that eliminates the space requirements of the drain P-traps under our sinks and shower. it also eliminates the need for a vacuum breaker or drain pipe vent plumbing in a stick home. A signifant advantage is that RV shower floors can be lower to the floor as the height space below our showers is not needed for the P-trap.
http://www.hepworth.co.nz/HepVo-Intro.htm (http://www.hepworth.co.nz/HepVo-Intro.htm)