We only had to drain Buttercup one time. I didn't follow sterile protocol like you did (good for you!) and just poked her three times in three separate spots (but close together) with the same needle. I just wanted to get as much fluid off of her as possible because at that time I didn't think she would make it through the night. The needle went in very easily and she didn't move at all, so I like to think it didn't hurt too much.
Since Peep is draining on her own from the needle site, I'd check periodically to see if fluid is still coming off her. We haven't had to drain Buttercup again since that night when she drained out all the way on her own while she was on the roost overnight. I have heard some people have to drain again every 4-5 months, so I'm keeping a close eye on her and feeling her every day to see if there is any more fluid, but so far so good.
Buttercup's vent did look normal. Pinkish and nothing protruding like you mentioned, so I'm not sure what that could be. From what I understand when they lay internally, the yolks get backed up and do get infected because they sort of cook inside the warm abdomen. They kind of get trapped and fester and do get infected in most cases I believe. The vet tested her fluid (she drew a tiny amount off her - only 1 cc - at the appt) and said it was full of bacteria and she had a nasty infection, so that's why she gave me the Baytril. That may have been the reason why she survived and seems to be doing well. But of course it is not a cure and there is probably still a bunch of egg yolk stuck inside her. It's like putting a band-aid on a gaping wound, but it bought her some more time.
Good luck! Keep us posted! You're doing a great job with her. It's evident that you really care.