Hi,
Below is a copy of a frognet message that I wrote a while ago. This is the same design that I was selling as NW frogfest, they work well and do not loose as much fog to condensation as the pvc based systems do. I decided on the Nalgene after trying many different types of containers. I hope this helps. The total price is about $35-$50
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I thought I would share how I constructed a ultrasonic fogger. I placed the ultrasonic transducer in a glad ware container or a nalgine bottle and then drilled 3 holes, one for the electricity for the transducer, one for air in and one for air out. I then inserted aquarium airline tubing into the 2 holes and hooked one end up to a air pump (the type that fish people use to run under gravel filters). This pump pressurizes the container and because all the other ways for air to escape have been sealed by silicone the air must go out the tubing on the other end. The result of this project is a very fine, visible mist that floats out of tubing into the tank. I experimented with different tubing diameters and found that thinner was better because then the air pump can clear it when the condensation on the tube clogs.
Alexander Stubbs