I always put my priming sugar in first, and lay the rackingline in the bottom of the bucket to facilitate it " swirling" as it fill. Brownian Motion
will take care of the rest. Just as a final precaution, I take a sanitized stainless spoon and ever so softly stir it. If you make waves, your doing too much. I simply follow the already swirling motion and reinforce it .
One thing I think many brewers do is rush through the transfer from fermentor / secondary vessle to bottling bucket. When I rack over a beer, I let it set for an HOUR in the bottling bucket - giving the priming solution plenty of time to get evenly dissipated.
Not saying that is the right way; not saying others ways is the wrong way . But I will say it works for me without fail, and bottle carb appears even through out the batches.