Really? Would you say ミルクが飲まない instead of ミルクを飲まない? After all, ない is an adjective.Astral Abraxas wrote:Grammatically 飲みたい is like an adjective though... for the same reason you don't say Ｘをむずかしい you don't say Xを飲みたい。
My own experience is limited, but from pretty much everything I've heard, there's nothing wrong with using を with -tai forms. Yes, some people, including native Japanese speakers, will recommend が, but by and large they're used with を nowadays.
Here is part 1 and part 2 of Tae Kim's take on the matter.