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The SatoPan seems to be quite well thought out, but I feel obliged to point out that this is virtually the same as a latrine devised by Dr Peter Morgan in Zimbabwe, which he called the WaterGate. Although it had already been patented by the Ministry of Health, he gave up on the idea when demonstrating that it was extremely robust by throwing a half brick down the pan and it broke the flap off. They were later copied in stainless steel in South Africa.
While the pan and flap look fairly robust, I remain a bit sceptical about the durability, but only time will tell. The bigger problem I think with this is likely to be the lack of a permanent water seal and so odour may be a problem.
I would recommend that you look at the PF pans that were developed by Ifo Sanitar in Sweden and are widely used in S Asia see https://documents.worldbank.org/curated/en/1985/01/1554646/design-pour-flush-latrines. These are designed for use in toilets where the structure is away from the pit and is designed to flush with 1.5 l of water. Having the toilet away from the pit, or pits has the advantage can they be emptied without disturbing the toilet slab. I suspect that the pan is very likely to be damaged if the slab has to be removed when the pit is full.
Whatever your chosen approach, I hope you can do better than the man in the SatoPan video when it comes to concreting. With a bit of control over the water:cement ratio, you could halve the cement content!
I hope that this helps with your search for a sustainable design.