I haven't found many info of tax declaration during deregistration, so here I share my experience (in Zurich):

Some days ago I went to deregistering.
After filling some basic info, I got a form of tax declaration and went to tax office (also in the cityhall) for signature.
I was told I need to pay the tax incurred during the months when I lived in Switzerland this year.
So the problem comes: the tax form will be sent to you after you leave Switzerland, BUT due to some reason, the tax form cannot be sent abroad. Therefore, I need to give an address of my friend who can reach me and send these forms to me in the future.
I haven't prepared for this issue, and it took me quite long to contact a friend and get the address.
Finally I signed a form to authorize my friend to open and check my mails concerning taxation.

So if you have the same problem as mine, plz prepare the following:
1. Before deregistration, obtain your friend's favor to help you and get ready with his/her address.
2. Upon your departure, plz prepare the relative materials that would be needed for tax declaration in the future.
Hope this helps.

PS: I really appreciate the lady in the tax office, who is very kind and very helpful. She even helped me with many instructions on how to fill the tax forms.

Alternatively, a "Treuhänder" can be paid to act in this capacity.

One can now complete the tax declaration online - presumably from anywhere in the world...

Thank you for the info!

Thank you for the info! This could save me much effort in the future.
Does "filling the form online" mean that you don't need an address to receive the form? Since there is a code of you when you want to complete the declaration online. Does the code keep the same through all the years?