[smeej]

Tasks are all handled as the same kind of object, but I'm going to call any task with a subtask a "project," and any task without any subtasks just a "task."

The way I would do this would be to basically treat "move the container" as a project and "empty container" as the first sequential subtask.

If you have: - Move container (sequential) | --Empty container

empty container will show up in the "Next" list because it's the "first" (only) subtask in the project. As soon as it's completed, the parent task, "Move container" will automatically show up on "Next" because it's now a task in its own right, not a project with subtasks.

This matches my intuitive way of thinking about how tasks relate to each other (do the parts, and when the last part is done, complete the project), but it's not done by naming something a "blocking" task.

Edited to add: I've not tried using it collaboratively, but I don't think that functionality exists. GQueues might be a better fit for that.