The bottle has a tube that runs through the lid and this makes it easy to turn them in to a Mariotte syphon. A Mariotte syphon delivers a constant rate of flow regardless of the liquid level inside the bottle.
I remove the top tube and then I make a small hole at the bottom and hot glue a piece of stiff tube in the hole. This then allows PVC tube to be attached.
Any soft plastic tubing will suffice. I buy general aquarium tubing from the local fish market.
Almost anything can be used as the splash tray/container. I have a thing for Chinese tea cups (my mother-in-law has some really nice ones). I have used baking trays, CD containers (the lids), bowls, glasses.
After I became more serious with water drop photography I had a couple of acrylic trays made. Ones is 80x40cm and the other is 60x30cm. I also bought black and white acrylic sheets to use as inserts.
To the liquid used in the reservoir (used for the actual drops) I add Guar Gum, this thickens the liquid. I mix a level teaspoon of Guan Gum powder to 1 litre of warm water. I blend this is an electric blender and then strain with muslin cloth to remove any bits. This gives me a cloudy thick liquid which I dilute with cold water as I use it.
To the water in the splash tray I add various detergents or cleaning fluids (I have tried lots of different ones). One that works well is natureclean’s All Purpose Cleaning Lotion. This works very well and was recommended by Corrie White sometime ago.
I have a couple of multi-voltage power supplies I use. I have these set to 13.5 volts rather than 12v. In the dropController, there is a 1N4007 diode on the vcc in line. The diode has a forward voltage drop of about 0.7v so the 13.5 becomes 12.8 after the diode. Driving the solenoids with a slightly higher voltage should be OK. Make sure you use one able to supply a decent current.
Be aware that actual output voltage from these power supplies can be quite different to what the label says. Another supply I have puts out nearly 16V when in the 12v setting.