I did mine in straight lines only up one side of the tube similar to this crude illustration which follows. So if you were to take the tube and look into it, the holes would run down the tube lengthwise in the 10 to 2 o'clock area. Then take a knife and cut a long thin square off of the Oasis foam, wittle it down until it fits comfortably in the tube. Or just run the tube down into the foam. Wet it down with the distilled water.
Distilled water is more mold resistant.
One to two of these will treat a large humidor perfectly, depending on where you live. Here's a great variation. This way if I put it in the center slot of the case, the two sides with holes point to the cigars on either side of it. Better than the one Humidif makes. I only used a small slice of sponge foam in this - it doesn't need that much moisture.