On the baking soda and vinegar, I just sorta eyeball it. I pour enough baking soda down the drain until I can’t pour any more, it will just sit there, and then I wet it down with vinegar. It will fizz!
After awhile, I will pour hot or boiling water down as a chaser to the other ingredients. Sometimes you can just pour a teakettle full of boiling water and it will take care of some minor problems.
Recently, however, the above solution didn’t work, so I got some Liquid Plumber Gel. That did the trick! It does have some toxic chemicals, but it works in extreme cases. I highly recommend it.