I am posting on behalf of a team of engineers designing a dry toilet for use in rural Nicaragua, as part of Engineers Without Borders www.ewb-sfp.org We are not sanitation experts so I will be posting a few questions here to get the advice of a more experienced community.
The toilets will use ash from cooking fires as the major additive.
How much capacity is generally needed in the vault for a family of four over the course of one year? (Based on a Latin American diet.)