This topic is occasionally discussed on the forums: Do low flush toilets provide sufficient water for adequate waste carry in the building sewer lines?? Well, some folks with lots of time and money on their hands have researched it, and botom line>>>no worries, mate! Here are the details:

http://www.cuwcc.org/toilet_fixtures...t_05-03-11.pdf

http://www.cuwcc.org/toilet_fixtures..._Rpt_08-05.pdf

http://www.cuwcc.org/toilet_fixtures...s_07-02-20.pdf