This is not an easy solution. You might investigate some of the composting toilets. You can try the internet or the links from this WEB page for leads.

The only other alternative I can think of is an aerobic system. This can be costly and would require permission of your local authorities, but the effluent from an aerobic tank is pure enough to use in drip irrigation of the yard. You can try the following WEB site for some additional information on this type of system, www.hydro-action.com