The bike was purchased used and I am just trying to get it going. I do not know what the previous owner did.
Ah, NOW it begins to make sense! This would have been good info in your initial post.
I've used XT/Icetech for over a decade on 4+ bikes. I've never had an issue with contamination on this system. The one time I couldn't resolve the squealing, it was a faulty brake that (I suspect) was slowly leaking fluid around the piston. It that case, it was continually contaminating itself.
That doesn't mean it can't happen of course, but the times I've had persistent noise was when one piston would extend with the other one stuck.
I recommend looking to see if this is the issue. If it is, you can free up the piston and that should solve the problem (and it's free).
If that doesn't work, then cough up the bucks and just get new pads and rotors. But look at the pistons first as it may save you some $$.
In the future, don't put anything on the pads/rotors prior to using them, as it will just boil off the water and deposit whatever is in the water (dawn detergent, degreaser, coyote sh*t, whatever) onto the pads. But, like I said, I've never had a noise issue that wasn't resolved either by adjusting the pads, or cleaning the pads/rotor with alcohol, other than the faulty brake. I've never baked, sanded, blowtorched, etc., any pads or rotors, but every once in a while I'll get detergent on them. But I rinse them pretty thoroughly after with plain water.
