I don't know if my method will work for all flavors, but you may want to try it. I flush out my carts at the kitchen sink. I begin with a mouth full of water, then lean over the sink and gently blow it through the cart. I do this a few times from both ends. I finalize the blow with air until the water quits dripping out. This doesn't remove all the moisture, so the filler has to be completely dried out before refilling.
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