The Coanda Effect is that a jet of fluid stays close to a convex or almost flat surface if it flows next to it due to pressure differences caused. In the case of this toilet, the set up means that a jet of urine stays close to the outside wall of the toilet and is separated from the solid waste, allowing the solid waste to be composted. There's an animated diagram at the bottom of this page
http://natsol.co.uk/urine-diverting-compost-toilets/ This article on the Coanda Effect as applied to air flow suggests some experiments for me to try
https://en.wikipedia.org/wiki/Coand%C4%83_effect
