B
Blunt Tool
They must wear their underpants on top of their trousers!I know this is not exactly the answer you were looking for, but you might consider getting a professional mastic man in to complete the task. Get your guy to remove all the grout from the transitions explained above, then get someone in that only does Silicon work for a living.
They are clean, fast, and above all very very neat. It will also lift the finish of your project.
Silicon work can make or break a job, it'll either look excellent, or very very bad.
It's something I always push for with my clients, because they always so much better than me.
And it's worth every penny, in my opinion anyway.