After building a hopper for one of my machines I was having trouble with the balls getting caught up in the PVC tube that fed the machines hopper. After a lot of time and experiment I have found that the best way to feed the hopper is to have the tube be larger than the hole in your hopper.

This would mean you would have to attach it from underneath. I used hot glue. With the tube being larger than the hole, this prevents the weight of the balls from being entirely on the full diameter of the tube.

Works for me!