[QUOTE=Mike Wilde;1554109 by shorting it though a 1 megohm resistor for a few seconds.
That will hardly begin to discharge a typical flash capacitor of 250 uF charged to 300 Volt
(See my earlier post)
The way it works is, Time constant [seconds] = Resistor {ohm] * Capacitance [Farad]
The capacitor will still have 33% charge (say 100V) after being discharged for one time constant so you have to leave the resistor on for about 6 times longer

Take care!