Macbrews,
I actually plan my length to allow a little loss in transfer, to make sure the keg is full (and then push a little more out to make some head space.) But you're right, when the noise stops it's flowing! I only use about 2psi so it does bubble vigorously, but the flow is really fairly slow. Anyway, thanks for the technique!
Another thing I've learned about the Speidel is that yeast harvesting is much easier than with a glass carboy; easy to pick it up, swirl and shake, and no worry about air contact.