Thanks everybody!

I just looked in the spout area and oh my goodness it's a nightmare. I managed to get most of it out with vinegar but there are some hard to reach spots and I ran out of vinegar in the process.

I think I will just throw that bottle away.

Funny thing is, it's the bottle I use for water. The bottle I use for my sugary drinks is fine. Only it smells a bit like grape, but i'm not complaining about that!