Downy liquid softener ball, could you fill this with vinegar?

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As I was responding to another discussion, I thought about this. We have one of those Downy fabric softener balls that I don't use anymore and I am always forgetting to add the vinegar during the rinse cycle. That ball is made to open during the rinse cycle, do you think that it would work? I had tried the ball with other brands of fabric softener and it seemed to work okay.