The standard filter will not fit through the Dubro type bung hole, or even the aluminium rings you can buy to make the tank fit more reliable, I made a custom clunk for a customer along with a tank to do this - the process was to take the pleated filter, I used one the same diameter as the small unit you refer to but twice the length so as to maintain a good filter length, cut the glued ends off, machined up some brass ends, one with an M6 thread to fit a barbed fitting to and hysol'd the whole shooting match together.

See picture of finished result.

PM me for info on where to get these filters.

marcs