If it's outside under the hot Australian sun I'd say paint the bugger white or silver, anything but black.
If it's outside you want to put a bigger tube around that tube that has an opening on the bottom and on the top. Something like a chimney tube. The top of the tube you paint black so it heats up. This will make a hell of a "chimney" suction effect and even 40 degrees hot air will manage to cool the steam down to condensate in no time. Black works awesome in the sun to create cooling effects if you use it the right way. Have a look at the colours the Tuaregs in the North African desert wear. Dark Blue and Black because it makes them sweat more and the fabric makes the sweat evaporate which cools.
The idea with a hollow water tank is also good but it isn't high enough to create the chimney effect. The evaporation would occur in the engine or right after the outlet because this is where the water is the hottest. This is why I mentioned blowing air into the outlet pipe to cool it down before it reaches the drum.
My general feeling is that you need 2 m height as a minimum to get a sufficient airflow in hot climates and the tube has to be coiled to create turbulences which enhance the heat transfer process.
In cold climates I would simply weld a 1 m tube to the drum because anything below 15 degrees ambient temperature will create more than enough condensation.
Cheers,
Edward
