Puzzle Idea: use tubes to redirect excursion funnels
Will do!
Ok what they did was they used something called a info_particle_system which referenced to an info_target). In the info_particle_system, it's value "Particle System Name" is 'blob_curve_orange' (I'm guessing this is why it curved so nicely). What is strange about this value is that you can open up a browser like the modelviewer for particle system types. The only thing is: is that nothing comes up. I guess that's why the Authoring tools is Beta a the moment.
In the level, when you actually get a bomb and blow up the side of the pipe it then activates blob_sprayers (i.e. the real gel that makes you slide).
So what they actually did was make an illusion that the gel is flowing through the pipes using a particle system instead of actually making gel flow through it.
The great thing about these particle systems is that they can be parented, same with the info_target it is referencing and turned on and off: so a pipe that moves along gel in a pipe puzzle is entirely possible.
Very cool, chicken. Thanks for finding that out! You should make a demo map with the flowing gel effect, I bet people could use that to make some pretty rad shit.
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I could upload one soon. All I need to do is put in some comments on how to make it curve nicely.
EDIT: I uploaded an example .vmf. Here's the link to the thread topic2798.html
awesome, the idea is possible 
I hope to see this in a map soon.