I read up on wikipedia that the Holiday Special episode (the one with recycling) apparently had a behind the scenes special. The only piece of it I could find on the internet was the sound effects portion: https://www.youtube.com/watch?v=5QYHlsskRmI
Know anywhere else I can somehow find it? Kinda sucks that they never added that part in the dvd or vhs.
Found it a few days ago :) It shows the entire behind-the-scenes process for each episode, from the pre-production/writing, to the voice talents, coloring and music, etc. I loved this show as a kid (this and Bill Nye were my favorite kids' science shows), so I got a real kick out of actually seeing the voices behind the animation. What struck me at first was how old the kid voice actors were! They were around 14-16 at the time of that episode (making them around, say, Kim Kardashian's age now), and they really did a good job of sounding 'young.' Their voices seemed so natural on screen but when you see it behind the scenes you can tell it takes a good effort to do it - they were well trained. I also didn't know that the Friz recorded in a totally separate studio from the kids - interesting. The show's long done, but it was nice to finally see how they did it!
Here's a link to that video, starting exactly at the part where they introduce the voice cast: