What do you use and describe your procedure.
Delboy can explain best..
Delboy's Garage, Brake disc and caliper wash out.! - YouTube
I usually pump the brake pistons out far enough to get to the crud around them but not far enough for the pistons to pop out. Then it's brake cleaner and a brush to clean them off the pistons.
This won't stop the squeeking but will help improve braking.
The squeeking is MOSTLY caused by pads that are vibrating very slightly when brakes are applied. To combat this, I put a little copper slip on the rear of the pad. NOT THE FRICTION SIDE! The side that touches the pistons. This will stop the squeeking.
Just a little dab.