Dear all,
I'm not a magician, I'm a woodworker. I have an idea for something which I would like help with please if you don't mind.
Imagine two different coloured liquids. One in a visible glass bottle, the other in a hidden reservoir/tank behind a wooden panel. From the front the observer simply sees a glass bottle full of a red liquid. The bottle is connected to a tap (faucet for my american friends), and when you turn the tap the liquid dispenses into a drinking glass below. The trick though is when the tap is turned the liquid which comes out of the tap is not the red liquid in the visible bottle but the blue liquid from the hidden reservoir. Meanwhile, as the blue liquid pours into the glass, so the red liquid drains through a hidden pipe down into a second hidden reservoir.
The finished contraption would look something along these lines (with modifications obviously)