At work we use a task for preparing the environment. It might be confusing for some people but the task we use is very much the same task as the task from a user story. The task does not belong to a user story but is estimated in hours and it has to be agreed on by the product owner to complete in a particular sprint.
We also use the task for architectural work that does not have an "apparent" business value but that adds quality to the product particularly for an existing product with a large code base.
These might not apply in your work environment but it worked well for us.
