To discharge capacitors, you really should use a resistor to do it.
Basically, you should short each of the big capacitors through the resistor until it measures zero voltage with a multimeter.
Don't ask me what Ohms or Voltage because it depends upon what you are discharging and how fast you want it to discharge. The voltage that the resistor can handle should be more than the voltage on the capacitor. The resistance (in Ohms) should be higher if you don't mind waiting or lower if you want to dump the power in a hurry and don't mind dumping some wattage through the resistor. I think that there are some web pages that talk about it in more detail.
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