The best way I have found to get rid of baby spit from formula is to use hydrogen peroxide. What I do is poor peroxide on stain, let it sit 5 minutes, then repeat. Once done I put the article of clothing in the wash and wash it withing the 2 days. The stain is gone.
Tried and True method for getting baby formula spit up. THe quicker you treat it, the better it comes out. This is the bast way I have yet to find, I work in an infant day care center, so I have plenty of opportunities to try new things out. This one is definately the best idea.