I have played with those. NOT all bottle caps are the same size I found out my self years ago. I did find that the 1" thin wall PVC works and seals tight. What I did was take a sample of the PVC to the store and try it on all of them. The cap size is the same for the small bottles as the larger one so you can mix and match the caps. Red coke caps I think fit the 1"thin wall PVC, but nothing fit the thick wall stuff that I found.

Good luck and the top return should keep them from running over when they get clogged.