I am currently working on Task A, which is currently estimated to end in 2 months. There are five other tasks in pipeline: B, C, D, E and F.
Task F is something I care very much about, because it is related to my previous work in the company. However, it is the least important one to my boss. I am planning to work after office hours and in weekend (unpaid) to complete task F.
How can I properly approach my boss about working on a low priority task?