To the OP
I have had quite a few darkrooms and today I have the best solution for water control.. I use very long 20 ft red rubber hoses connected to a normal shower head control you can get at Home Depot. the head can have a thermostate between the input and the hoses.
It also can have a splitter for two hoses.... at the end of each hose I have on one a shutoff valve (Home Depot) the other I have just cut the hose.
This situation is perfect for me as one can walk the hose around the room if needed , clamp the hose to different areas, the hose is heavy duty rubber and one is actually tough enough to walk on .. $150 bucks at most , I would never , never again buy a high price water panel and would never ever hardwire plumbing to a sink again..
I use this system each day and when needed drag the hoses into a second sink in a second room to work,,,