My clients usual questions…
Does the propane tank have to be empty to re-certify?
The propane tank must have zero pressure inside for re-certification. This is essential, because a valve must be removed from the tank and be replaced in the process of re-certifying your tank.
You would know that the tank is completely empty when your appliance connected to the tank stops running. If you do not have anything connected to your tank, connect an appliance to the tank to drain it.
I would like to let you guys know that it is unsafe to vent to the atmosphere.