The reason for not using the screw driver to discharge a capacitor is because the printed circuit board or circuitry can be damage due to the spark make while release the high voltage capacitor. I one time blowed the power section using this way. Though, if you know that the capacitor stored voltage is not too large, you can simply discharge it with a small screw driver. if the capacitor holds a heavier charge of power. Discharging the capacitor may melt the tip of the screw driver and the copper on the printed circuit board.

Place the leads of a socketed 100 watt electric bulb on the leads of the capacitor this method had been used by a lot of technicians around the world for the light bulb will act as an indicator to see if the capacitor still holds the charge. If there is a charge the light bulb will light and after discharged the light bulb will goes off.

Place the leads of a high wattage resistor on the leads of the capacitor. I use a 2.2k ohm 10 watt resistor to discharge the high voltage capacitor in a switch mode power supplies. It is easy to use and very efficient