Cluttered, but the flashes are moved around to front to see them. For clear water drops, the flashes go a foot or two BEHIND that frosted acrylic panel (off camera, far left, behind the pole).
Some of this stuff is pretty high tech, that is a 5 gallon paint stirring stick and a couple of clamps to hold the frosted panel to the black pipe. Normally the frosted panel stands in the water at the rear of the pan. You can see the frosted plexiglass panel between black pipe and lower flash. This setup was used for all the pictures on the previous Shako page, except the flashes were a couple of feet behind the frosted panel, aligned vertically like this, but much lower to the water surface. Horizontally, flashes, water splash, and camera lens all on a straight line. Vertically, nearly so, but splash was maybe 8-10 inches lower. Angle of incidence is equal to angle of reflection. You need a LONG pan, 18 inches is skimpy for a low camera angle, however at that length and low angle, more length really doesn't help that much. The Mariotte siphon is behind the top flash now. I use a longer tubing on it to allow raising and lowering it a bit.
The flash mounting bar is just 8 inches of 1 x 1/8" flat aluminum bar stock from Home Depot. Two 1x1 inch pieces of it were used as spacers under the Shako solenoid valve. This bar simply has three 1/4" drilled holes, for two Stroboframe+flash+shoe and the center support. Any flash shoe with mounting hole should work (using a standard UNC 1/4"x20 screw), even those flat plastic stands provided with the Nikon flash. But the Stroboframe shoes are exceptionally good.
I use two Nikon SB-800 flash, with PC sync cord to one from StopShot, and an Ebay SC-18 cord (Nikon 3 pin cable) between them, acting as a Y connector (shown). This Nikon 3-pin cable is obsolete now, designed for TTL on film cameras, but the SB-800 has these connectors too, and they work (for manual flash mode here). There are also regular PC sync Y connectors on Ebay. A flash without a PC connector (SB-700) will need a foot mounted accessory shoe which adds a PC sync connector, Here or Ebay or from StopShot (INSTEAD of the Stoboframe shoe - be sure it has the screw hole under it). Some of these foot adapters have two PC sync connectors, which can provide the Y connection for a second flash.
For the flash, I use a regular light stand with a mini boom on it (Smith Victor and Impact mini-booms are the same, I think), and an Impact umbrella mount ... stuff I already had. The umbrella bracket should work on top the stand without the mini boom. It provides angular tilt, rotation, and clamp.
Color filters for flash are THESE or THESE. I use the first, it has a few more... but hundreds of color filters in either, sized to tape onto the flash head (I use masking tape). These Rosco swatch books may be available free from your local camera store if you ask them. See Other Uses for them. Here is a description of the filters in the first RoscoLux swatch book. If using high flash power, you want to bow the filter slightly (see the blue one?) to leave a tiny air gap under filter so they don't melt (1/32" - just no direct contact), but low water drop powers do not matter.