How to pay property-related tax after moving out of Belgium?

When you decide to leave, you go to the commune to de-register. At that time you complete a form known as a "modele 8". That form gives your new address abroad. Although the commune shares this eventually with the tax authorities, there is no reason that you shouldn't also send a letter (perhaps with a copy of your completed "modele 8") to your tax office. If you're leaving before the end of the year, you probably also want to complete a tax return, as you may also be due some rebate on your income tax.

Keep a bank account open ONLY for ALL immobilier / rent income & expenses.
set-up a domiciliation / SEPA order linked to that account.
..also for insurances etc and pay attention, that you have always a minimum amount EUR in that account (or set-up payment reminders in your calendar/s)

Running with this system since years - no problem.
Good luck, xl

Hey XL, how do you make your tax declaration if you have a property here in Belgium but you live abroad and have no access anymore to your ID card needed to login to the tax portal and do it online?

I am asking for a friend who recently moved abroad. Maybe the answer is also useful for the original poster of this thread.