I have two girls with sour crop (Welsummers) that apparently got it from eating too much grass. I didn't know the upside down vomitting method at first, but once I found out, I have tipped them upside down several times to get the gunk out. I have to actually squeeze the gunk out, and they don't fight and seem to know it is a good thing because they actually calm down rather quickly. In fact, I just had to isolate one of them again because she was looking so bad and her crop was distented again. I tipped her, squeezed out what I could without hurting her and she actually got some color back in her comb and wattles within a couple of minutes. She wants to eat, but she is on the water w/ACV diet for 3 days then it will be yogurt for 2 or 3 days and then I will add starter crumbles to that for a couple of days and then start letting her eat other feed. I do think that I am going to have to open and clean both of these girls out, but I hate to think about it. It is going on too long and neither of them is very much more than feathers and bones anymore from this.
I hope yours goes better than mine are.