I got so sick of fiddling with my needle valve all the time, I decided to do something about it. For around $300, I purchased a used Cole-Parmer Masterflex pump, a new head, and all the tubing / fittings required. These units are made for continuous duty and have a great reputation for running for years and years with quarterly tubing replacements.
I was using a maxi-jet pump in the sump (I have also tried the unit gravity-fed) but I would have to adjust the needle valve daily. I hooked the unit up pulling through the reactor on the effluent side. I am hoping to avoid blowing the lid off if the effluent line clogs. These pumps can build up high pressure, and I don't want that kind of pressure in the reactor.
Here is a video of it in action. I checked the output and it's dead on. The numbers bounce around a little bit, but I continuously measured 35-40mL per minute through the unit. Now all that's left is to clean the installation up someday, it's kind of ghetto right now.
http://www.youtube.com/watch?v=foMimmngyjM