[Sean Marconette]

I would suggest installing a blowdown on the bottom of the tank. It could be a timed 120 VAC solenoid, or as simple as a ball valve that you manually open. Moisture will kill the tank, as it will rust from the inside out. With the hot and humid air from the attic, fabricating a source of air to the compressor may also help. In the industrial and commercial HVAC world, with pneumatic controls, oil and water has to be reduced and eliminated. So for your tires and pneumatic tools, I would not spend the money on an air drier. Keep your pneumatic tools oiled, and eliminate condensed moisture in the tank.

I would pipe down from the attic, and install a tee. Out of the bottom of the tee, a 6" or longer nipple, and ball valve. This would be a blowdown to help separate any moisture. On the other opening of the tee, a regulator, and you are set. On the blowdown you can reduce the diameter to 1/4" copper and run it outside. Keep everything from the tank line size until the regulator. So if the tank fitting is 3/4", all piping should be 3/4" until the regulator. Reduce down at the regulator. This will not restrict the air volume.

Sean