I am new to nitrous and I was just reading Timberwolf's thread entitled "$40...wasted". I dont know what this disk is you guys speak of. I feel stupid.

 

there is a pressure relief disk that installs on the side of the valve,to vent pressure before the bottle explodes.

unless the car has a sealed trunk,you have to use that with a blowdown tube to vent the nitrous outside of the passenger compartment.