I have used a 1 Gallon Milk bottle and a 1/2 gallon milk bottle and they work great too. Instead of puting one of the holes in the side i just drilled two 1/4" holes in the lid and had 2 hoses coming out the top. The 1 Gallon bottle made a huge difference in the ammount of humid air being fed into the tank. Also be sure not to have to hose that lets the air out in the water, the positive pressure from the air pump will force water into the tube.

Happy Buiding