He used the Clean Mountain Can. Made in the USA, it is a portable toilet; an 11 inch high plastic can, weighing 2.4 pounds, with an opening that is eight inches in diameter. Inside it has a gas-impervious insert bag designed to keep in smells ( why worry up there?) and neutralise the waste inside.
Now he is going public with the device and urging all climbers to use it: "It is portable and very secure. I want to promote anything that manages human waste on the mountain.There is a heightened need for environmentally friendly practices in climbing, not only to have a neutral impact on the mountains but a positive impact." :: Reuters
More on Mount Everest's Clean-Up
Sherpas on Everest Highlight Climate Change
Cleaning up Mount Everest