boyo, standard water drain systems crack open the drain at 3-5 psi. If you wanted this to work really well, just plumb in a solenoid valve that works off the same circuit as your timer from the other post. When the timer goes off for the night, it closes the outlet from the tank. Then the downstream system will leak down and the water drain valve will open and pee water all over your floor. Of course, you should design in some leaks so that your system will bleed down after the solenoid valve shuts.
