Hi mjohnson - if you're still around, I'd like to hear more about your aquarium pump solution. Was the pressure / flow rate good enough that you still get quick cooling? It seems like a pump would pump out water slower than a faucet does, but I guess that depends on how powerful it is.
Also, did you need any extra parts to attach it to your immersion chiller? Or did you just push one of the barb fittings into the plastic tubing on your chiller?
The reason the pump solution interests me is that my sink doesn't have a removable endcap. I could buy a new sink head, but hardly any modern sink heads come with threaded endcaps anymore. If you want a nice looking sink head, especially the spray nozzle ones, it's not going to have a threaded cap. So a pump in a 5g bucket might be my best option.