For example, there's some add-on task like marketing advertisement artwork or internal task like upgrade computer. it's not in the flow but it took WIP slot of that employees. Just sometimes that it need to be done not always for that work. What should I do about this task? It may not be directly customer value but it took WIP. At this time I just use different post-it color to visualize and when it's done, I just took it off without take it to next flow step.
Kanban is all about visualizing your process as it is, at least to start with. So, if your main process has some work-items that occasionally have 'sub-tasks' or add-on tasks as you say, then that is real work that should also ideally be visualized on your Kanan board, especially since it is using up your available WIP limits for specific employees.
Ideally, in order to make sure you have a good handle on how long these add-on tasks take - and you manage their execution/ completion well, you can have a simple sub-lane for them to manage their cycle-time easily. See the example below -
This way, you are not only able to highlight to your team but also to your stakeholders that there is additional work that your team is having to do - but that it takes available capacity. This should help you ensure that your team is not overloaded.
Depending on whether you are using a physical board or an electronic Kanban tool such as the one shown below, you should be able to link the main task in the top lane to any add-on tasks it may have in the lower level lane.
On a physical board, you can just use a different colored sticky on top of your main work-item and another on the add-on task and perhaps number them the same so it is clear to anyone looking that there is a dependency. An electronic Kanban tool can give you a dependency link feature that helps you track the add-on tasks easily and track them to closure on multiple ways.
Either way, Kanban helps you do 3 key things -
- Visualize all the work that your team is called upon to do
- Enable you to allocate WIP limits to all streams of work and do work as per those WIP limits. So, in fact, you MUST define a WIP limit for your add-on tasks as well
- It helps you highlight your team's work and its loading effectively to everyone concerned so no undue demands are placed on the team.
Hope this helps!