When I was at Everest Base Camp with the British Mount Everest Medical Expedition in Sept. and Oct. of this year we used one of our 40 litre blue barrels as a toilet (only for "number 2's"!!).
When it was full the environmental scientists (lucky people, but it was their choice of career!) emptied it out on rocks and let it freeze dry, then replaced it. We ended up with less than one barrel, weighing only about 35 pounds to be shipped back to Kathmandu for safe disposal (we averaged about 15-20 people at base camp over a period of nearly 3 months).