Unless steps are taken to seal the chamber/bucket, or a fan is added to the vent stack, would a draft be created? Are there any articles on this?
Given that a typical toilet seat is less than airtight, and that there is going to be an airgap between the bucket and the seat, it seems like the system is basically open. I checked my toilet seat here at home, and there is a 5/16" gap between the bowl and the seat, and a 1/4" gap between the seat and the lid. My toilet seats would have approximately 17.5 sq in of ventilation just at the bowl/seat/lid area. A 3" vent pipe would only add 7 sq in.
I guess my question is whether the juice is worth the squeeze. A lot has been made of the fact that composting toilets don't smell. The prevalence of vent stacks seems to suggest otherwise. I guess I can try without and always add one later.