There has been considerable discussion on this topic, and I've tried a
number of different approaches. Most were mediocre at best.

Butyrate dope thinner works remarkably well. After scraping the labels
off (I use a dull hunting knife after soaking), a bit of the thinner on
a paper towel removes most of the remaining stuff in one pass!

A quart would do dozens if not hundreds of bottles. Available at
aviation maintenance shops that work on fabric covered aircraft.