It should be in primary until about 1.020, because that's when fermentation begins to slow down and could be vulnerable to oxygen. (Up until then, stir the must a couple of times a day, breaking up the "cap" on top, if there is one.) Rack into secondary, removing all the banana pulp and skins, and leave all the sediment on the bottom of the primary if you can. Then go ahead and use an airlock.
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