CAM 5 LASER CUTTER : needing to change the laser tube
What you want is called a discharge stick, and your best bet is to buy one. (http://www.tomwblack.com/phenix/40400_Discharge_Ground_Sticks.pdf)

If you're hell-bent on doing it quick and cheap, then you can try this.

What you do is take a wooden dowel or fiberglass rod about 1/2 to 1 inch in diameter, and about 18 inches long. At one end you make a series of 10 1M, 1/2 watt resistors, with the lead of the end resistor sticking out. The resistors are epoxied to the rod, and then held in place with tie-wraps. You really want a mechanically strong unit. From the resistor near the center of the rod, solder a wire of a convenient length, say 12 - 18 inches long, and put an alligator clip on it. Put down a rubber mat and stand on it. Have someone who cares about your health (like you) use a meter to verify that the resistor chain from exposed wire to alligator clip is 10M, and not open. Check twice. Connect the alligator clip to chassis ground. Holding the end of the rod in one hand, put the other hand in your pocket. No, I'm not kidding. Now touch the exposed resistor end to your high-voltage connection, and let it sit there for at least a minute. 

Keeping the resistor in contact with the HV, have somebody else measure the voltage. Assuming it's good, connect the HV and ground to the meter via secure clips, and monitor the voltage when you remove the resistors. You'll probably see a certain rebound. Now clip a 1k, 1W resistor from HV to ground to bleed of this rebound.

And you should be good to go. 

Of course, you want to remove the 1k before you turn the unit back on.