I needed a pump for a viscous fluid in one of my projects and it seemed a no brainer to uses ttsalo's version http://www.thingiverse.com/thing:15538
However, I have been hitting a wall in my tests and when discussing the matter it was pointed out that stator should be made of rubber to provide a tight fit with the rotor so cavities are sealed while moving.
Not having elastic filament at hand nor experience on how rubbery it might be, I asked around. User A2 suggested on reprap forums http://forums.reprap.org/read.php?180,112397 to use oogoo silicone, which I did not know but it's just a google away.
I've built a sample stator and matching rotor pump for a test and it works nicely.
I modeled the cavity of the rotor, which can later be screwed it out from the silicone once cured.
The funnel-like part can be used to contain the cavity you are modeling with oogoo silicone and act as the stator.
These are some videos of its operation (forward)
Print both parts. I used the top of a Listerine mouth wash as a container for the stator. I filled it with ooogoo silicone (1 part of corn starch and 1 part of silicone, add a bit of oil-based color if desired).
Then I screwed the cavity part out of the cured stator hours later.
Now the pump is ready for action: insert the rotor and rotate it. Please note some play is needed so the motor will need to leave some play for the rotor top to go side to side.