I've been thinking about everything since I had two infected beers. I bought a new bottling bucket before I found the suspected real cause of the infections. Previously I just left the bung hole in the lid opened as I bottled. I used plain water to experiment with using an S-style air lock in the lid of the new bucket during bottling. The vacuum created with the spigot completely open sucked the Star San solution out of the air lock into the bottling bucket. The flow rate was greatly diminished when using the bottling wand on the spigot and filling a bottle. With the S-style air lock filled to just below the maximum fill marks there was no suck back during bottling.
I'll probably go with the air lock on the bottling bucket from now on.