Yes Jason, I'm amazed you are already going after double run emulsions
Yep, that's me. I had to try it. When I sit here at work waiting for the code to build or one of those "endless" meetings, well, you kind of zone out sometimes and ...

I figure there's enough to keep me occupied with SR and SRADs for a long time..
Yeah, don't be in a hurry. As PE has told us, there is more to this than meets the eye. Not that making a double-run is that hard, mind-you, but there are so many variables involved that it is hard to be able to tell what you might be doing. Eventually, though, over the long term it is probably the way forward.

Silver plating is always a nuisance to keep in mind. Happens with glass stopcock burets, too. It's important to keep things rinsed out.
I noticed the buildup after my last double run. I've made three. Two worked, in that I got a working emulsion although it wasn't anything special. One was an outright failure, except I can use it for coating practice. Fortunately, they were all quite small. The needle should clean out easily enough, and if it doesn't, they are pretty inexpensive.

I assume the reason to go with such elaborate tools as hypodermic needles is the hope that they will give you extreme precision
No, not really. I was looking for two things, a smaller orifice to help slow down the flow rate thereby making it easier to add reactants over, say, a 20 minute period in a relatively constant stream. And second, as a way to bring the entry point of the reactants into proximity for mixing purposes. The first they achieve, the second they do not. The initial idea was to bend the needles to bring them together, but that doesn't work because you cannot bend them, or at least not easily without breaking them. So the idea switched to using tubing. I think Chris' idea is better than mine, though.

There are adapters made that are female luer-lok to tubing and tubing to male luer-lok.
Will have to look for this sort of tubing. Sounds like a solution.

... and standard tubing goes over a Luer male connector on a syringe and can be cut to any length and clipped in any position.
Another possible solution but will have to find tubing of the right size. I would guess it's available but never looked.

Things on the photography front at my house have had to take a back seat lately. My available time has mostly been spent playing with the Mamiya 645 so have a little time to figure out the next steps.

-- Jason