Paula Begoun makes a clear scent-, conditioner- and antibacterial-free shampoo
that works well for cleaning my Swift and humidifier tank. I just dilute a little in the sink and soak the parts.
I was already using this as my daily hair shampoo, so my skin is already used to it - good thing for me as I can get contact eczema. Anyway, I think it's worth a try for CPAP-cleaning purposes. I'm not too concerned about the trace amount of cocoa butter; it's pretty far down the ingredient list, and the "no buildup" claim is true.