De or het douanebehandeling?

The correct Dutch article is:

de douanebehandeling

Rule Words ending in -ing: almost always de. See the rule

How to use douanebehandeling

the douanebehandelingde douanebehandeling
this douanebehandelingdeze douanebehandeling
that douanebehandelingdie douanebehandeling
our douanebehandelingonze douanebehandeling
your douanebehandelingjouw douanebehandeling
every douanebehandelingelke douanebehandeling
which douanebehandeling?welke douanebehandeling?
a big douanebehandeling / the big douanebehandelingeen grote douanebehandeling, de grote douanebehandeling