I've done the tub thing before and found it to be a major pain in the .... back. Now I take bottles and set them upright in buckets. Then I heat up (usually I'm re-heating) some PBW in my electric kettle and fill the bottles and bucket (fill bottles first or they will float). The next day I empty the used PBW back into my kettle to be re-heated, rinse the bottles, and do another batch. I usually do three buckets at a time since my kettle is 15 gallons. This system works so well for me that I use it for every empty bottle, not just ones that need the label removed. Sure, its overkill, but I have piece of mind knowing that on bottling day there isn't a single speck of filth in any of my used bottles.