I've tried the coke and mentos thing and found that a 6mm hole drilled in the bottle cap works very well.
 
I was presenting my Exploding Custard show right next to Eepybird and their diet coke extravaganza at the Centre for Life last spring. Their warm, sugar-free liquid certainly rose higher than my own balls of fire and drips from the ceiling were clearly visible. Andy Lloyd will correct me if I'm wrong but I think the American presenters reckoned on reaching a height of 30 feet. I also recall that the ceiling height was 29 feet...
 

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From: psci-com: on public engagement with science [mailto:[log in to unmask]] On Behalf Of Gemma Hebden
Sent: 06 July 2009 10:09
To: [log in to unmask]
Subject: Re: [PSCI-COM] Explosion help!

:
I have also been corrected by the teacher who confirms the coke reached at least 20 feet.
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