Hey Andy, warm water and soap is about as good as any. You need a good set of brushes though to get inside, also some very light action steel wool works for rust spots and around embossing on the exterior. Search the forum a little bit, has been tons of post on cleaning bottles. Outside of a tumbling machine your options are limited. Muratic acid works O.K. but not worth the hassle of buying it and the fumes are very nasty. I usually soak my dug bottles in 5 gallon bucket of dish soap and warm water for about a day, and brushes are very handy to get inside. Pettydigger
i asked a similar question ahile back on this site. barkeepers friend was recommended to me and it works very well. as pettydigger advised search the forums on this site and you will find alot of very useful information
Soaking in a 50% purple power 50% water solution seems to be ok.. you can get a 2.5 gallon jug of purple power at advanced auto for about 10 bucks. On my sodas and small neck bottles, i use a gun cleaning kit, you can buy various size copper tips, its like a mini round copper wire brush. and they have the cloth tips too. For those nasty rust stains inside, try wrapping a lil bit of fine steel wool around one of the copper tips. walmart has the gun cleaning kits for around 10 bucks. extra tips are about 2 bucks. MY biggest problem is, i want to (dig now and clean next week)lol...Xcali.
barkeepers freind is like 2.97 at walmart in the household cleaning section its hard to spot look around for the ajax and junk it will be right around it