In case you forgot, that's Urine Diverting Dry Toilets. A friend in Ecuador pointed me at a blog of a usano who has been in Ecuador for decades. The blog is specifically about UDDTs and seems like a good fit for Nicaragua.
While there is more Spanish than English in the blog, recent entries are in both languages. What is offered is practical experience with low tech approaches using recycled materials. While it was not what I was looking for, it clearly is about as close as you can get to a free UDDT. In areas with a high water table, it looks like an easy solution to an almost impossible situation.