how to empty FX Impact air tank for shipping

I appreciate all the input. Will be offering it in classified section soon and just wanted to get my ducks in a row. Perhaps I am overthinking it. I thought USPS had restrictions on shipping charged air tanks. Thanks all

I ship guns with air still in the bottle. It's inside a cardboard box. How would ups or FedEx even know what's inside. They have no rights to open it and see what's inside. Just paid the fee and they will ship it. 
 
I’ve received guns via both FedEx and UPS and they’ve always arrived with air in the tanks. In fact, FX uses FedEx for their warranty work and ships rifles back to their customers with air in them so I’m sure it’s fine if you do the same.

USPS may be different because they put a lot of priority mail on airlines but if you use UPS or FedEx ground it’ll be fine.
 
I believe air rifles can only ship with empty tanks. Is there a way to empty the tank on my FX Impact other than dry firing? Is dry firing OK for the gun?

All five PCPs I have ordered arrived with pressure in the reservoir. Only my JoeB fill tank arrived empty. I have sold three PCPs and shipped each with pressure. If it's a real "requirement" the shippers appear to not police it.