Hey Julian,
Here's a link to the post I've seen a peristaltic pump being used:
The maker doesn't go into a lot of detail, but you can get the general idea.
You can find a lot of these pumps by searching "dosing pump" on eBay.
From my understanding, for dosing low amounts you probably want, it's best to get one for the smallest diameter tubing.
I bought a second-hand medical pump myself, I think they are normally used for IV transfusions, for about 60 EUR, it's called Gilson Minipuls 2.
A bit bulky compared to the cheap one from eBay, but everything is integrated, and provides a very wide range of adjustment via a multi-turn potentiometer and very smooth flow due to using 10 rollers instead of 3.
Even though you didn't ask for it, in case anyone is interested, here is my other collection of links on FogBuster-style DIY systems:
Cheers
Gene
