We inherited a couple here where we live. One is in a turret (like a castle
) it has a timber seat, you pea or poo as normal then you have a shovel and some nice fresh wood shavings you pour on top to stop the smell (roses in my case
). The ones we have are just buckets below the seat so you can then transport the contents to somewhere else once there is a build up. You can have one you have steps up to so you can have a compartment below or a big composting bin which you can remove the contents over time, or I've seen a diagram somewhere for a double one - a two compartment if you like so it takes longer to fill.
I'll try and get photos on of the ones we have - at least for entertainment value