my doc allowed me to wash my hair once my "hat" was removed (24 hours post op) but said I had to hold a styrofoam cup over the site so it didn't get wet. Not having any stryofoam cups in the house, I used a plastic one, and that's how one ended up in the Official BAHA Recovery Kit. It's kind of awkward to hold a cup on your head while you shampoo, but well worth it. I personally hate dirty hair - gives me the creeps (the 9 days I had to wait after my AN surgery were horrible)
As we always say, docs have different rules, so you are right to check with yours before shampooing even with the cup.
The Dawn is for the hair washing also. Once you start putting bacitracin or neosporin on your site, your hair gets gunked up very quickly. The Dawn cuts the grease - a tip we got from Lori. She's a nurse in real life so to my knowledge this isn't a dangerous practice.
Glad the pain is minimal; it typically is.