The main drain line wasn't a problem simply because of the weight of the water and the distance that it falls, it's able to force the air out the end. It was the gentle falls, such as from my collection container down into the skimmer and fuge tubs, which only falls about 3 feet through 1 1/4" pvc pipe. I guess they were big enough that air would get trapped in them and the flow was slow enough that it would very effectively block the flow down those pipes until the water got high enough in the 35g collection container to push the air out. It did overflow once on me when I first got it working so the drill quickly came out and a small hole was drilled ABOVE the water line to give the trapped air a place to go. Problem solved.
I drilled a very small hole in the elbow and yes, water does dribble out of that hole occasionally but I drilled the hole so the water then drains into the skimmer/fuge tubs anyway so it's not a concern for me. I was just flabbergasted that it stopped the flow of the water.
This is all based on my experiences and we have two very different solutions so just because it happened to me does NOT mean it WILL happen to you. I was just offering my experiences.
