• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

ambient release

There's no need to discharge a tube, per se, as tubes don't store charge.
The power supplies, however, can make you use words that your mother wouldn't approve of...
If you want to discharge the power supply of a tube piece of equipment, use a high value resistor to short B+ to ground. You can permanently install bleeder resistors if you like, but keep in mind that it will waste current that you might prefer to use elsewhere.
Me? I don't use bleeder resistors. If I intend to fiddle with a piece of equipment, I use a meter to check the voltage on the power supply caps. If I'm too lazy to get a meter and check the voltage the proper way, I usually end up getting a pretty good reading through my fingertips. The volume and duration of my cussin' is carefully calibrated to the amount of voltage I get via my fingers.
For those who are afraid of the voltage in tube equipment, I'll simply note that I've been shocked more times than I can count. It hurts. You cuss. You feel stupid. Go on with the next thing. I suppose it's not recommended for those with pre-existing heart conditions, etc. but it's not like everyone who touches live voltage immedately rolls over with four paws in the air.
But be careful, just to be on the safe side. No need to play hero. It's just a hobby.