J,
For cleaning teak, I used Snappy Teak for over 15 years until I went to a composite material.
You want to do MINIMAL sanding on your teak to save the wood. If your wood is weathered, yea more sanding will be needed.
Snappy teak is a two part cleaner. I had used others, but this was the best I found. There are probably other good strippers, but I found the ST to be easy work with only "knock-down" sanding required afterwards. Just follow the directions. Note, part two is the acid coat, so wear gloves and do not let dry on your deck. When rinsed with water, it neutralizes. When dry, the teak will look light sandalwood. Your first coat of varnish will bring out the beauty of the wood, just like instant sex.
It is a little harder to find, my last batch was ordered online.
CR