I'm lacking on the scientific reasons why vinegar works so well, but a very high percentage of the people here use it. There are a few people who know all the PH levels of the various products and can tell you why it does what it does. Anyway, vinegar is awesome. If you do a search, there are very extensive discussions on this topic asking what the best way to clean mf is. The vinegar acutally helps disolve the left over detergents, thus leaving the towels softer and cleaner than without. I don't use a dispenser or anything, just let the washer fill up and pour a little right in there. I was told to only use the 5% distilled white vinegar which happens to be the stuff at the grocery, very cheap. I even use a little vinegar in my regular washes every now and then to give them a like new feel again. You would be surprised at how much detergent is left in your clothes after washing.