The way I treat the birds is to flush out the crop with a Turkey baster full of slightly warm water with probiotics in it. I will fill the crop a couple of times and squeeze it empty till all the material is out of the crop and the crop is nice and clean. if your bird has bound it's crop with larger grains you might as well forget it, because those are almost impossible to get out. If you have trouble with sour crop, I would highly recommend feeding only pellets to your birds because pellets turn to mush in the crop and are easily squeezed out. If not pellets feed only very small grains. But even with very small grains it's very difficult to flush them out. But it is easy to flush out pellets.
Once you flush a bird's crop is when the work starts. At this stage it's vital to prevent it from immediately reoccurring. It will immediately reoccur because the bird will be very hungry and thirsty because his crop was just bound for a day or two and he is famished and if allowed will gorge himself on food and water when given a chance. Say you treat the bird in the morning, put him back in the loft and see he's fine and you go to work but when you come home he is bound up again! It's discouraging and you might blame the bird but it's your own fault, not his. Once the crop is flushed, you have to give the bird very small amounts of food and water multiple times per day until enough food and water can be left in front of him till he won't gorge himself on it again. This normally takes a couple of days
For proper prevention you need to make sure all the birds have free access to food and water. There are many reasons a bird won't eat even if food and water is available but only in one location. One is aggression. You might have an aggressive bird guarding the food or water and that may keep a bird from eating and once he does get a chance he will gorge himself. That's why it's wise to have multiple feeding and watering stations in the loft.
Another cause of sour crop is Pigeon milk binding the crop. When the milk forms in the crop of a pouter it lines the crop and makes it heavy, that in combination with food and water will send many large cropped breeds over the edge. It's risky letting large cropped breeds raise their own or even sit long enough to form milk. If they make it past the milk stage, there's another danger and that's feeding the young. A bird may gorge itself to bring back food for it's young, thus causing the crop to bind. Personally, I always use fosters and never allow them to even sit on eggs more than a week for fear the milk will be formed in the crop.
I have some pictures of crop bound birds but I can't find them right now. If I can find them I'll post them. But it's easy to spot a bird that's crop bound, but you need to be careful because sometimes when they mope they will go into a dark corner and you don't see them till it's to late.
I only have problems when the weather gets hot from June-September, that's when they drink a lot more water.
I also never breed two birds together that have had to be treated. It might be superstition but I believe there's something to it genetically. I have some birds that never get it and some that are chronic. Maybe it's the way they hold their crop or it's physiological, I am not sure but I sure don't want to pass it on to future generations if I can avoid it. I would like to retire all chronic birds from the breeding loft but some of them are so nice, it's hard to do.
Response by Rene Kruter: I only feed whole grains and therefore I gave up on washing out the crop. My method is the old fashion one. I role the bird in a newspaper and place it, head up, in a PVC waste pipe of 90 mm. After 12 to 24 hours the crop is empty and the recovering as you describe can start with minimal feeding a few times a day.
Alan: How do you tie the bird down in the newspaper so it can't move?
Al Neese: Alan, you just Roll the bird up in it a tape it.
Rene: Yes, Alan, legs backwards, crop up and roll it in a newspaper. It will automatically be a bit tapered and from the top you can check if the bird is relatively comfortable.
When the temps are 110 F or so here in the desert I have problems with a few certain birds over drinking, so I have started to dock the crops of a few of the chronic cases described by my friend Rene Kruter. Below is a picture of a newly docked crop. I wet the feathers and pull them from the area of the crop to be docked. I pull a piece of about 1" of skin at the lower or middle part of the crop and rap a rubber band around the skin I want removed. The blood circulation will stop and the skin will fall off over a period of time. It is supposed to be painless for the bird and he won't have anymore problems. They eat and drink they please without a problem. This only removes a portion of the front of the crop. It does not effect the digestive tubes. The crop size is reduced but it still keeps it's basic shape.