Oxy Clean is definitely the way to go. I have a ceramic sink so I can just use that but if your sink is metal I'm pretty sure a long soak is bad for metal. If that's what you have use a fermentation bucket or rubbermaid instead. The following method works for me:
[1] Scoop out some Oxy Clean and dump it into your container (bucket/sink/whatever...).
[2] Fill container with warm to hot water, enough to cover the bottles. I like to add the Oxy Clean first and then use my sprayer to get it nice and mixed up.
[3] Add your bottles and make sure they are completely submerged.
[4] Leave to soak overnight (if possible). The longer the better.
[5] Usually the lables will literally float off. Any slight amount of goo left behind will almost rinse off but if not, just use a normal kitchen scrubby-sponge and it will take no real effort to get clean...almost a wipe.
[6] Thoroughly rinse all of the bottles...and then rinse them again.
[7] Let them dry upside-down for a while and they'll be ready to store until you are ready to use them.
NOTE: As others before me have mentioned already, your bottles are clean but NOT SANATIZED. You still need to sanatize before filling on bottling day.
I do this at least once a week to prep my empties in advance. Every saturday night after a group emptying session
we put the empties in the sink and the last thing I do that night is start the Oxy soak. They're ready for me by morning.
Hope that helps!
-Tripod