My outhouse is more-or-less a defacto composter. It's dug into the middle of a stand of mature willow and spruce, and it sits on a shallow trench so I can pull the composted material toward the back with a discarded garden rake.

I add a few leaves or sawdust after each visit, or a bit of fresh wood ash and charcoal, to reduce flies and smell.

I plan to add an old eavestrough in the front to direct the "liquid propulsion" to the shallow roots of the adjacent trees. This is primo fertilizer, and it represents most of the infamous outhouse smell that people recoil from.

And, I plan to add a "solar wall" in the back, with a tall vent pipe, so that gases/odour are directed back and out, instead of up through the hole when you open the lid.

Aside: I should mention that I've been making and experimenting with charcoal. There is no more effective substance for eliminating odour in toilet facilities. I used a five gallon pail filled with firepit charcoal for a week as a urinal (in the interests of science). No smell whatsoever. None.