[MagnusWootton]

If you place the stick inside,  put the tacky on the end,   if you try to pull it out, itll suck back inside the tube/straw.

I'm making this,   this afternoon in about 4-5 hours, and ill see if it does what I'm predicting.

My computer I want fully mechanical, but I'm thinking of employing pneumatics for the power supply,  I want to see if I can make a vacuum switch on and off with a light weight valve.  I'll see how it goes.

[infurl]

https://en.wikipedia.org/wiki/Fluidics

Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.

While you're on this train of thought, you should check out fluidics for some ideas. It uses the movement of fluids to implement logic and control circuits and is a proven technology with a long history.