I had two cases of sour crop with 2 squabs from the same clutch. I tried messaging and forcing the food out of them and flushing the crop with baking soda and water. I used a syringe with a small piece of tubing attached. Long story short I lost both squabs. I may have had better luck if I had detected it earlier. They were fully feathered and on the floor of the loft and beginning to peck on their own.