Place the onions in a quart jar with a tight fitting lid. It might be necessary to pack them down pretty hard to get them in there.
In a small bowl. combine the hot water, cider vinegar, sugar, and salt. Stir until the sugar and salt have dissolved. Pour the liquid over the onions - enough to cover them fully. Place the lid on and refrigerate overnight, at least. Keep refrigerated. The red color on the onions will fade and the onions will turn a light pink. Serve on burgers, hotdogs, bbq sandwiches, by themselves, you name it! They're even great on tacos!
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