Looking back on it (it's been a while since I used it), I think the best way to fill it would be to get a (new) turkey baster & use that. The instructions suggest using a piping bag, but because the batter is so runny it made a huge mess - for me at least. I ended up using a spoon but I still had batter everywhere.
-Lisa
I have done a few, even though I don't like them. I found using two cake mixes works best. I make the extra batter into cupcakes.
I use an extra large pastry bag and binder clips keep it closed in between pans.
I does help to have an extra pair of hands to hold the divider rings firmly in place.
Looking back on it (it's been a while since I used it), I think the best way to fill it would be to get a (new) turkey baster & use that. The instructions suggest using a piping bag, but because the batter is so runny it made a huge mess - for me at least. I ended up using a spoon but I still had batter everywhere.
What a great idea on using a baster. I would have never thought of that. Now I actually have a use for that thing besides letting my daughter play with it!
Are you all using the plastic divider ring set? My grandmother used to try to tell me how to do this using wax paper as a divider! I've never made one, but am hoping to get the set for C-mas this year, but I CANNOT IMAGINE HOW HARD THIS WOULD BE W/WAX PAPER! Of course, Mammie is a genius at this stufff......ahem....I get my talent from her.....
(honestly I do) 
I've never used the funny pan and dividers....bake a chocolate round and a white round and After they are cooked torte them and then with a sharp knife cut circles in them like a bullseye the gently pull them apart and exchange the circles and restack them to get your checkerboard effect...much easier I think...
thanks everyone.
I think that the turkey baster is a great idea!
I did use two cake mixes, but i think that i way overfilled the pan, leading to not straight lines and running out of batter.
it was the first time i used pudding in the mix and boy it does make the cake so much more dense and moist!
thanks again!
I have yet to use mine. I'm glad I read is post or I'd be saying, "what the heck!" 
This from Wilton tells the batter measurements for each part, maybe that'll help...
http://www.wilton.com/recipes/recipesandprojects/hallween/howcandycornisborn.cfm
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