Water to the Neck in Ten Minutes

You all stand ankle-deep in a sealed chamber, and the water is climbing one finger every minute — ten minutes and it swallows the ceiling. Three valves, a padlock coded in colors nobody agrees on, and a diagram half-eaten by the flood. Turn the wrong valve and the flow doubles; you have exactly one guess to spare. One of you spotted the real code the moment you entered and hasn't said a word — hoarding the way out for a private deal. The tallest among you buys the shortest maybe two extra minutes, no more. Talk fast, split the tasks, and choose: who dives for the diagram and who breaks the silence, before the count says none of us make it?