Hjohnson215 seems to have the right idea. Another way to exfoliate is to use an alpha-hydroxy cream or lotion. It dissolves the dead skin cells that are clogging the pores and the clogged pores contribute to the acne. It is a product you should test on your skin in a small amount first to be sure you are not sensitive to it. This worked well for my son, but he said it stung a little on the open acne. He was happy with the results and it was much cheaper than the acne treatment products you see on television.
The rubbing alcohol only disinfects the acne, it does not open the pores. To open pores you use lukewarm water or steam, to close pores you use cold water. But if you want to get rid of back acne you will want to exfoliate at least 2-3 times a week to get rid of the dead skin cells and use a acne wash (preferably one that is created for your body). In the past when I had some breakouts on my chest or back I used dial soap or Neutrogena Body Clear Body Wash. But it all depends on your skin and hormones. You may have to experiment to find the best result for you or you can go see a Dermatologist who can prescribe a medication wash for you.