Sang thats how a lot of folks degas them. Put your sanitized hand over the top and shake it. Remove your hand and it will poofff. When it stops pooffing, it is good to go.
Some take a large plastic stirring spoon and shave the head down to fit the gallon jug and use a cordless drill on them.
I've done both, the drill one is quicker, but potentially more prone to eruptions.