You need to wash in a non-bio washing powder or liquid to remove the stains etc. The white vinegar just helps to eliminate some of the smell. You can put the vinegar in the softener compartment of the machine.
To wick the fleece so that the urine passes through you do need to wash with detergent 2/3 times on a hot wash cycle 60 degrees or preferably 90 degrees. Once it is dry pop a towel under the fleece and pour a little water on it, it the water soaks through your fleece is ready to use, if not wash it again. One of the fleeces I had recently took like 6 washes to wick, but I worked out it was due to a softener build up in the washing machine, so I put the machine on a clean cycle first (might be useful if you are having problems).