The big improvement was replacing the surgical tubing with fish tank tubing from the pet store. A chemist friend tipped me to the fact that with just a little Vaseline, the fish tank tubing will slide onto 6mm OD glass tubing we are using and make a great seal. That seemed to work great, was cheap, and was much easier to work with. I also increased the inverted NH3 catch flask size from 250mL to 1000mL. That should make for a better looking fountain.
In order to detect when the flask was full of NH3 I used a clothespin to clip a litmus paper inside the flask stem. Last time we just bombed the flask with way more gaseous NH3 than needed. It worked, but was inelegant. The idea with the paper was filling the flask to have just enough gaseous NH3 to work. Turns out the paper is hard to read when reacting to gaseous NH3.
It turned out we filled up the flask partially with ammonia – but nowhere near as much as we needed to draw enough vacuum to trigger the fountain, just enough to trigger the litmus paper. The whole point of these projects is to get a better feel for physical chemistry, and practices at the lab work. So I did learn a lot, but it was still frustrating.