Yes. Turning the cold water tap on is what creates the suction to pull water from the tank. Once started however, you can (as George was saying) stop the tap water and continue draining the tank water though more slowly, and this can run down the sink. I know that a few times when I have disconnected the Python from the tap to use the tap to rinse the filter and the other end was still in the tank, it continued to drain the tank but very slowly. If the "drain" is lower, say outside, then it would presumably be faster.
Byron.