Did you notice that each time you buy LN2 there is an environmental fee on the invoice. Seems like it goes up each time I refill
Anyway, it's there to cover the costs of properly disposing of unused LN2 in your Dewar. Remember, this is LN2 you already paid for (unless you're Kiki).
Propper disposal method according to the EPA is dispersing into the atmosphere
So, you have to pay this regardless if your dewar is full or empty. It's a complicated maneuver of opening the vent valve until no more gas leaves the dewar
I can see why they need special training to do this, can't you
