I use bar keepers friend for the first try of cleaning the glue off. then I use lighter fluid as last resort 93 octane gas. I have found that one of these will cut the gunt off. Yes be carefull with the second 2 but I do end up with clean exterior bottles to be refilled by me. The best is once they are mine I use rubber contact cement to put my lables on. They will stay on forever but they will peel right off after i have emptied a bottle. or if a little stubborn bar keepers will work with a small brush and its ready for refilling.