I had problems with air bells on my film and got rid of them by making sure I tap the tank, firmly, several times.
Previously, I was a bit hesitant to hit the tank too hard for fear of cracking the plastic or denting the metal tanks because my processing area is an old style, cement laundry sink. I was afraid the hard surface would damage things.
The solution to the problem came at the suggestion of another APUG member: Use a rubber mat.
You could use an old mouse pad or whatever but I use a 12" square piece of rubber floor mat.
Now, I can rap the tank as many times as I need to, almost as hard as I want, and I don't have to worry about hurting anything. Having the mat also reminds me to tap the tank often.
Not sure this is your solution but I think it makes an interesting aside.