Either would work.
If you want to put it in the tank, which IMO is the safest during a power outage. I would do it like this.
Get a cylinder style container such as a 3 liter "yes 3 liter" soda bottle. The cut the bottom of the soda bottle out then get a circle bubble disk that same diameter as the soda bottle. Then cut slices in the side of the soda bottle and discard the cap. Fill the soda bottle one half full of ceramic rings, then attach the bubble disk to the bottom of the soda bottle. Plug it in and let it go.
Now the bubbles come out of the bubble disc evenly through the whole soda bottle, the water is sucked into the bottle and through the ceramic rings, from the slices on the side. The air and water tries to rush out through the small opening at the top of the bottle, this forces the air and water into a stream causing great surface agitation then just a bubble disc.
I say this is safes during a power outage as the bio media will always be wet, and well feed, and will likely not sit in stagnate water. You could also hook up the bubble disc to a battery air pump.
You could also go smaller scale and use a 2 or 1 litter bottle and smaller disc style bubble disc.