I mix vinegar and baking soda when cleaning the drain. I do it on a regular basis to avoid experiencing worse problems in the future. So far, it works. I avoid the use of chemicals drain cleaners too.
Definitely 100% silicone. Don't use siliconized latex.
If you need color matched caulk the silicone Latisil by Laticrete is great stuff, but you need to go to professional tile stores to buy it,
