--Please only urinate into the front separator (smaller hole).
--Toilet paper can be put down the larger hole.
--If used, please always throw 3 scoops of sawdust down the larger hole.
--Please avoid any sawdust getting into the front urine separator.
Composting toilets have been around for a while -- you'll find them in rural areas of Europe and North America where there's no sewer service and where for one reason or another a septic system can't be installed. But Totoco's toilets are not composting toilets in the usual sense; the composting is done elsewhere. The solid waste and sawdust go into a big bucket that twice a day is emptied into a compost area somewhere out of sight of guests. It wasn't apparent what happened to the urine that is so carefully kept separate.
There was no odor -- either in our own bathroom or in the toilets shared by the dining room and the hostel. Totoco -- there's a link in Ometepe item below -- has a handful of cabins like ours and eight or so hostel beds in a large room beside the dining room. If you're going to stay at a hostel, it's hard to imagine one with better views, nicer common areas (there's a pool) or more interesting toilets.