One of my older dogs has developed a problem which I think may be Megaesophagus. I have been to the vet twice now and reported that he was bringing up a gooey type of bile and they didn't seem at all worried. Over the last week or so my boy has been bringing up bile more often, especially after drinking and it seems worse overnight. He occasionally brings up his food but much less often. Could it be Megaesophagus?

http://www.peteducation.com/article.cfm?c=2+2090&aid=848

This is an article about megaesophagus, they usually regurgitate their food shortly after eating.

Hi
I have a 2 yr old girl who was found to have Megaoesophagus as a pup when she started to be weaned. She has had two Barium Swallows which showed hers to be a probable problem with the nerve development serving her oesophagus and it has improved with age and management although it may always be a bit of an issue.
I manage her eating upright on a soft diet and she rarely regurgitates food but when she does it is not bile but undigested food as with MO the food doesn't actually get as far as the stomach acids so it doesn't start to digest. Also when she regurgitates she doesn't make all the noises a vomiting dog does - it seems to take her by surprise (thankfully she hasn't done this in over a year).
From what I know of Megaoesophagus I would say it is unlikely your lad has it if he is mainly bringing up bile. I wonder if he would benefit a trial on having more frequent small meals to lessen the build up of stomach acid??? I hasten to add I am no vet but maybe worth a try.
Incidentally MO in an older dog is usually a symptom of something else as opposed to the primary condition but I still think it unlikely this is the problem in this case.
Hope you can sort him.