We could have an airtight cover on the opening to the toilet. This
will keep the smell from leaking into the main cottage area except
when someone inside/the lid is opening. The lid can automagically
opened by a foot pedal or the opening of the door when someone enters.
This could go a long way in terms of suppressing the smell inside the
poo cottage I think. The poo tank would always be vented to the
atmosphere of course.
I will sketch up some ideas for this.
nils