In a 3.5 game I'm in right now, I'm playing a Duskblade with a Hippogriff familiar. As Hippogriffs are quite large, I'm getting worried as to whether it will fit through small spaces or narrow hallways in caves or dungeons without being a bother to the rest of the PCs. I can't seem to find any information to explain how this works, and I'm very curious about it. In addition, I've been reading Order of the Stick, so Blackwing's constant disappearing and reappearing has been confusing me even more. 

Are familiars always present, or are they able to appear and disappear when needed?