Robert, just so you know I have brand new tubes and have modified my towers so that the light is in a metal tube that fits perectly to the outside diameter of the bubbling tube and it still takes some time for the bubbling effect to start. This includes both the K-Line Bubbling Tower and the much smaller bubbling tubes that are typically commercially available around the holidays: I've used those too for my own creations.
So here's the little trick I discovered long ago with no ill effects: I use a small dental type hook (that also comes in handy for other train functions) and I gently tap the tube once or twice and the bubbling effect starts right up. A small mini hobby screw driver would work as well. Again, I've been doing this for years with no trouble.
But let me note I do mean just a gentle tap is all it takes. You don't want to use something bigger like a full size heavy screw driver and accidentally hit the tube hard enough that it breaks.