How to properly discharge a high voltage capacitor?
A resistor is called for. If it's charged to 300V and you want to limit the current to 1-2A you need a 150-300 ohm resistor. DX has a suitable Dale-style 100W 200 ohm resistor for less than $4 including shipping, or you can get a genuine one for a bit more. 

Peak power will be 450W 



But a typical resistor of this type rated for 100W continuous can handle about 100J pulsed, and you have at most CV^2/2 = 7.6J. 



As always, check that it actually is discharged before handling (and after that, maybe short it just to be double sure). Note that because of dielectric absorption, capacitors that are discharged briefly can appear to re-charge themselves somewhat. Probably not an issue with such a low voltage, but it can be enough to cause a jolt on high voltage capacitors.